Geologi Sejarah [PDF]

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MAKALAH



GEOLOGI SEJARAH Diajukan untuk memenuhi tugas ujian akhir semester mata kuliah Geologi Sejarah



DISUSUN OLEH : HASBI FIKRU SYABI 270110140101 E



FAKULTAS TEKNIK GEOLOGI UNIVERSITAS PADJADJARAN TAHUN AJARAN 2015/2016



CONTENTS 1 CHAPTER 1 INTRODUCTION A. Time…………………………………………………………………………..



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B. Geologic Event Record……………………………………………………….



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A. Fundamental Principles of Gelogy……………………….………………… B. Unconformity………………………………………………………………..



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CHAPTER II GEOLOGICAL TIME A. B. C. D.



Earth’s Age………………………………………………………………….. Radiometric Dating.. ………………………………………………………… Geological Time Scale………………………………………………………. Catatrophism and Uniformitarianism ……………………………………...



13 15 18 20



CHAPTER III PALEONTOLOGY A. B. C. D. E. F. G. H. I. J.



Fossils………………………………………………………………………… Invertebrates Fossils…………………………………………………………. Fossil Preservation…………………………………………………………… Fossil and Evolution………………………………………………………… The Law of Faunal Succession…………………………………………….. Natural Selection…………………………………………………………….. Evolution…………………………………………………………………….. Darwin’s Laws……………………………………………………………….. Dinosaurs Extinction………………………………………………………... KT-Boundary………………………………………………………………….



23 24 25 26 28 29 31 32 33 35



CHAPTER IV PLATE TECTONIC AND GEOSINCLIN A. B. C. D. E. F.



Geosyncline Theory Development………………………………………….. Plate Tectonic Theory Development………………………………………… Plate Movement………………………………………………………………. Basin and Plate Tetonic……………………………………………………… Mid Oceanic Ridge…………………………………………………………… Seismic Zone………………………………………………………………..



39 40 42 45 49 51



CHAPTER V THE ORIGIN OF THE EARTH A. B. C. D. E.



The Origin of The Universe………………………………….……………. The Solar System………………………………………………………….. Earth Crust Composition………………………………………………….. Geosyncline………………………………………………………………... Plate Tectonic………………………………………………………………



52 53 59 60 62 1



F. Plume Theory……………………………………………………………… G. Big Bang Theory……………………………………………………………



64 66



CHAPTER VI PRECAMBRIAN A. General Information……………………………………………………….. B. Division Precambrian……………………………………………………… C. Evidence and Fossil Record in Cambrian……………….……………….. CHAPTER VII PALEOZOIC A. Cambrian…………………………………………………………………… B. Ordovician…………………………………………………………………. C. Silurian……………………………………………………………………… D. Devonian…………………………………………………………………… E. Carboniferous……………………………………………………………… F. Permian……………………………………………………………………..



75 76 80 82 85 89 93 96 99



CHAPTER VIII Mesozoic A. Triassic…………………………………………………………………...... B. Jurassic…………………………………………………………………….. C. Cretaceous………………………………….............................................



102 106 107



CHAPTER IX CENOZOIC (TERSIER) A. B. C. D. E. F.



Definition…………………………………………………………………. Division…………………………………………………………………... Tektonic and Paleoclimate………………………………….………….... Biota Evolution…………………………………………………………… Hominoid Development in Cenozoic…………………………………… Quarter Human Development……………………………………………



111 112 116 117 119 119



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CHAPTER 1 INTRODUCTION A. TIME Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them. Time is often referred to as the fourth dimension, along with the three spatial dimensions. Two contrasting viewpoints on time divide many prominent philosophers. One view is that time is part of the fundamental structure of the universe a dimension independent of events, in which events occur in sequence. Sir Isaac Newton subscribed to this realist view, and hence it is sometimes referred to as Newtonian time. The opposing view is that time does not refer to any kind of "container" that events and objects "move through", nor to any entity that "flows", but that it is instead part of a fundamental intellectual structure (together with space and number) within which humans sequence and compare events. This second view, in the tradition of Gottfried Leibniz and Immanuel Kant, holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be travelled. Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities. Time is used to define other quantities such as velocity so defining time in terms of such quantities would result in circularity of definition. An operational definition of time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as the second, is highly useful in the conduct of both advanced experiments and everyday affairs of life. The operational definition leaves aside the question whether there is something called time, apart from the counting activity just mentioned, that flows and that can be measured. Investigations of a single continuum called spacetime bring questions about space into questions about time, questions that have their roots in the works of early students of natural philosophy. 3



B. GEOLOGIC EVENT RECORD The geologic record event in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata — deposits laid down by volcanism or by deposition of sediment derived from weathering detritus (clays, sands etc.) including all its fossil content and the information it yields about the history of the Earth: its past climate, geography, geology and the evolution of life on its surface. According to the law of superposition, sedimentary and volcanic rock layers are deposited on top of each other. They harden over time to become a solidified (competent) rock column, that may be intruded by igneous rocks and disrupted by tectonic events. Most of what we know about our planet's history is based on studies of the stratigraphic record—rock layers and fossil remains embedded in them. These rock records can provide insights into questions such as how geological formations were created and exposed, what role was played by living organisms, and how the compositions of oceans and the atmosphere have changed through geologic time. Scientists use stratigraphic records to determine two kinds of time scales. Relative time refers to sequences—whether one incident occurred before, after, or at the same time as another. The geologic time scale shown in Figure 4 reads upwards because it is based on observations from sedimentary rocks, which accrete from the bottom up (wind and water lay down sediments, which are then compacted and buried). However, the sedimentary record is discontinuous and incomplete because plate tectonics are constantly reshaping Earth's crust. As the large plates on our planet's surface move about, they split apart at some points and collide or grind horizontally past each other at others. These movements leave physical marks: volcanic rocks intrude upward into sediment beds, plate collisions cause folding and faulting, and erosion cuts the tops off of formations thrust up to the surface. Our understanding of Earth's history and the emergence of life draws on other scientific fields along with geology and paleontology. Biologists trace genealogical relationships among organisms and the expansion of biological diversity. And climate 4



scientists analyze changes in Earth's atmosphere, temperature patterns, and geochemical cycles to determine why events such as ice ages and rapid warming events occurred. All of these perspectives are relevant because, as we will see in the following sections, organisms and the physical environment on Earth have developed together and influenced each other's evolution in many ways. C. FUNDAMENTAL PRINCIPLES OF GELOGY Traditional Stratigraphic Laws are basic principles that use in deciphering the spatial and temporal relationships of rock layers. These laws were developed in the 17th to 19th centuries based upon the work of Nicolas Steno, James Hutton and William Smith, among others. Stratigraphic laws include the following: 1. The Principle of Superposition



Fig. 1. Bedding are superposotion In undisturbed strata, the oldest layer lies at the bottom and the youngest layer lies at the top. Steno (1669) states that : "At the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed." Law of superposition explained that in a layering of rock, most under the age of rocks is always older than the rocks above. This happens because the most rock bottom sediment first, and then formed into the stone, followed by a layer thereon. In fact the field, this law does not explain how if a rock has experienced very strong folds, or experiencing a reversal.



After a rock 5



experienced a reversal, it would violate the concept of superposition because the upper age of rocks older than the rock beneath it. If this happens then we can conclude that the law of superposition applies only to rocks that have not been deformed. 2. The Principle of Horizontaliy



Fig. 2. Horizontality Horizontality is a law that states all sedimentary rocks are originally deposited horizontally. Sedimentary rocks that are no longer horizontal have been tilted from their original position. This law was developed by Steno (1669), he states that : "Strata either perpendicular to the horizon or inclined to the horizon were at one time parallel to the horizon." Steno, 1669. In most situations where sedimentary layers are deposited ( for example, on the floor of the ocean or a lake or on the floodplaom of a stream), the layers are horizontal or close to horizontal. This observation is expressed as the law of original horizontality. Steno reasoned that strongly tilted rocks did not start that way, but were affected by later events, either upheaval by volcanic disturbances or collapse from beneath by cave-ins.



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3. The Principle of Original Continuity



Fig. 3. Original Continuity Horizontal strata extend laterally until the thin to zero thickness (pinch out) at the edge of their basin of deposition. This law was developed by Steno (1669), he states that : "Material forming any stratum were continuous over the surface of the Earth unless some other solid bodies stood in the way." Steno, 1669. The law of original continuity explained that on a rock layering, layers are continuously sustained even if the parts of the layer has been eroded or experiencing tectonic intrusion or experience. This bedding sustained not only in the scale of a few meters, but sustained until the end of the basin boundary. 4. Srata Identified by Fossil (William "Strata" Smith, 1816)



Fig. 4. Strata Identified by Fossil This law explains that, in each layering of rock would contain the fossils themselves and will vary with other bedding. this is because of the time



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difference deposition, which may have occurred several extinction of a species. 5. The Principle of Cross-cutting Relationships



Fig. 5. Cross-cutting Relationship This law was developed by Charle Lyell (1797-1875), he states that : "If a body or discontinuity cuts across a stratum, it must have formed after that stratum." Charle Lyell (1797-1875) An event that cuts across existing rock is younger that that disturbed rock. This principle is essential in studying all kinds of rocks, not just sedimentary ones. With it we can untangle intricate sequences of geologic events such as faulting, folding, deformation, and emplacement of dikes and veins. This law of explains that the case of cutting either in the form of intrusion or other, these rocks cut will always be older than the rocks are cut off. this happens because if a rock intruded by other rocks, the rocks are definitive formed first, otherwise it can not be a rock that intruded.



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D. UNCONFORMITY Concept unconformity first proposed by James Hutton (1785), in his ideas about the geological cycle (gelogical cycles). Unconformity is uncontinue vertically evidence of sedimentation, caused by tectonic symptoms (such as: folding, kemudiann followed by removal / orogenesa) or symptoms of tectonic lifting and tilt or solely appointment only / epirogenesa.) The term unconformity later develop into various types, such as: 1. Angular Unconformity



Fig. 6. Angular Unconformity An angular unconformity is a type of unconformity in which younger sediments rest upon the eroded surface of tilted or folded older rocks, that is the older rocks dip at a different, commonly steeper, angle than do the younger rocks. The unconformity surface may be essentially planar or markedly irregular. Angular unconformities may be confined to limited geographic areas (local unconformities). By or may extend for tens or even hundreds of kilometers (regional unconfo ties). Some angular unconformities are visible in a single outcrop. By contras, regional unconformities between stratigraphic units of very low dip may not be apparent in a single outcrop and may require detailed mapping area before they can be identified.



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2. Disconformity



Fig. 7. Disconformity Disconformity An unconformity surface above and below which the bedding planes are essen-tially parallel and in which the contact between younger and older beds is marked by a visible, irregular or uneven erosional surface is a disconformity Disconformities are most easily recognized by this erosional surface, which may be channeled and which may have relief ranging to tens of meters. Disconformity surfaces, as well as angular unconformity surfaces, may be marked also by "fossil" soil zones (paleosols) or may include lag-gravel deposits that lie immediately above the unconformable surface and that contain pebbles of the same lithology as the lithology of the underlying unit. Disconformities are presumed to form as a result of a significant period of erosion throughout which older rocks remained essentially horizontal during nearly vertical uplift and sub-sequent downwarping. 3. Paraconformity



Fig. 8. Paraconformity Paraconformity A paraconformity is an obscure unconformity characterized by beds above and below the unconformity contact that are parallel and in which no erosional surface or other physical evidence of



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unconformity is discernible. The uncon-formity contact may even appear to be a simple bedding plane. Paraconformities are not easily recognized and must be identified on the basis of a gap in the rock record (because of nondeposition or erosion) as determined from paleontologic evidence such as absence of faunal zones or abrupt faunal changes; In other words, rocks of a particular age are missing, as determined by fossils or other evidence. 4. Nonconformity



Fig. 9. Nonconformity An unconformity developed between sedimentary rock and older igneous or massive metamorphic rock that has been exposed to erosion prior to being covered by sediments is a nonconformity. Nonconformity surfaces probably represent an ectemded period od erosion.



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CHAPTER II GEOLOGICAL TIME A. EARTH’S AGE The age of our Earth is about 4.54 billion years. This dating is based on evidence from radiometric age dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples. Ancient rocks exceeding 3.5 billion years in age are found on all of Earth's continents. The oldest rocks on Earth found so far are the Acasta Gneisses in northwestern Canada near Great Slave Lake (4.03 Ga) and the Isua Supracrustal rocks in West Greenland (3.7 to 3.8 Ga), but well-studied rocks nearly as old are also found in the Minnesota River Valley and northern Michigan (3.5-3.7 billion years), in Swaziland (3.4-3.5 billion years), and in Western Australia (3.4-3.6 billion years). These ancient rocks have been dated by a number of radiometric dating methods and the consistency of the results give scientists confidence that the ages are correct to within a few percent. An interesting feature of these ancient rocks is that they are not from any sort of "primordial crust" but are lava flows and sediments deposited in shallow water, an indication that Earth history began well before these rocks were deposited. In Western Australia, single zircon crystals found in younger sedimentary rocks have radiometric ages of as much as 4.3 billion years, making these tiny crystals the oldest materials to be found on Earth so far. The source rocks for these zircon crystals have not yet been found. The ages measured for Earth's oldest rocks and oldest crystals show that the Earth is at least 4.3 billion years in age but do not reveal the exact age of Earth's formation. The best age for the Earth (4.54 Ga) is based on old, presumed singlestage leads coupled with the Pb ratios in troilite from iron meteorites, specifically the Canyon Diablo meteorite. In addition, mineral grains (zircon) with U-Pb ages of 4.4 Ga have recently been reported from sedimentary rocks in west-central Australia. The Moon is a more primitive planet than Earth because it has not been disturbed by plate tectonics; thus, some of its more ancient rocks are more plentiful. Only a small 12



number of rocks were returned to Earth by the six Apollo and three Luna missions. These rocks vary greatly in age, a reflection of their different ages of formation and their subsequent histories. The oldest dated moon rocks, however, have ages between 4.4 and 4.5 billion years and provide a minimum age for the formation of our nearest planetary neighbor. Thousands of meteorites, which are fragments of asteroids that fall to Earth, have been recovered. These primitive objects provide the best ages for the time of formation of the Solar System. There are more than 70 meteorites, of different types, whose ages have been measured using radiometric dating techniques. The results show that the meteorites, and therefore the Solar System, formed between 4.53 and 4.58 billion years ago. The best age for the Earth comes not from dating individual rocks but by considering the Earth and meteorites as part of the same evolving system in which the isotopic composition of lead, specifically the ratio of lead-207 to lead-206 changes over time owing to the decay of radioactive uranium-235 and uranium-238, respectively. Scientists have used this approach to determine the time required for the isotopes in the Earth's oldest lead ores, of which there are only a few, to evolve from its primordial composition, as measured in uranium-free phases of iron meteorites, to its compositions at the time these lead ores separated from their mantle reservoirs. These calculations result in an age for the Earth and meteorites, and hence the Solar System, of 4.54 billion years with an uncertainty of less than 1 percent. To be precise, this age represents the last time that lead isotopes were homogeneous througout the inner Solar System and the time that lead and uranium was incorporated into the solid bodies of the Solar System. The age of 4.54 billion years found for the Solar System and Earth is consistent with current calculations of 11 to 13 billion years for the age of the Milky Way Galaxy (based on the stage of evolution of globular cluster stars) and the age of 10 to 15 billion years for the age of the Universe (based on the recession of distant galaxies).



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B. RADIOMETRIC DATING Radiometric dating (often called radioactive dating) is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they formed. The method compares the abundance of a naturally occurring radioactive isotope within the material and the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale. Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied. That is : 



Uranium-lead dating method The uranium-lead radiometric dating scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. An error margin of 2–5% has been achieved on younger Mesozoic rocks. Uranium-lead dating is often performed on the mineral zircon (ZrSiO4), though it can be used on other materials, such as baddeleyite. Zircon and baddeleyite incorporate uranium atoms into their crystalline structure as substitutes for zirconium, but strongly reject lead. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very



14



chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. In situ micro-beam analysis can be achieved via laser ICP-MS or SIMS techniques. One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a halflife of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of the age of the sample even if some of the lead has been lost. This can be seen in the concordia diagram, where the samples plot along an errorchron (straight line) which intersects the concordia curve at the 



age of the sample. Potassium-argon dating method This involves electron capture or positron decay of potassium-40 to argon40. Potassium-40 has a half-life of 1.3 billion years, and so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in micas, feldspars, and hornblendes, though the closure temperature is fairly low in







these materials, about 350 °C (mica) to 500 °C (hornblende). Uranium-thorium dating method A relatively short-range dating technique is based on the decay of uranium-234 into thorium-230, a substance with a half-life of about 80,000 years. It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 34,300 years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sediments, from which their ratios are measured. The scheme has a range of several hundred thousand years. A related method is ionium-thorium dating, which measures the ratio of







ionium (thorium-230) to thorium-232 in ocean sediment. Radiocarbon dating method Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years, which is very short compared with the above isotopes. In other



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radiometric dating methods, the heavy parent isotopes were produced by nucleosynthesis in supernovas, meaning that any parent isotope with a short half-life should be extinct by now. Carbon-14, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth. The carbon-14 ends up as a trace component in atmospheric carbon dioxide (CO2). An organism acquires carbon during its lifetime. Plants acquire it through photosynthesis, and animals acquire it from consumption of plants and other animals. When an organism dies, it ceases to take in new carbon-14, and the existing isotope decays with a characteristic half-life (5730 years). The proportion of carbon-14 left when the remains of the organism are examined provides an indication of the time elapsed since its death. The carbon-14 dating limit lies around 58,000 to 62,000 years. The rate of creation of carbon-14 appears to be roughly constant, as crosschecks of carbon-14 dating with other dating methods show it gives consistent results. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon-14 and give inaccurate dates. The releases of carbon dioxide into the biosphere as a consequence of industrialization have also depressed the proportion of carbon-14 by a few percent; conversely, the amount of carbon-14 was increased by above-ground nuclear bomb tests that were conducted into the early 1960s. Also, an increase in the solar wind or the Earth's magnetic field above the current value would depress the amount of carbon-14 created in the atmosphere. These effects are corrected for by the calibration of the radiocarbon dating scale. C. GEOLOGICAL TIME SCALE



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The geological time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history. The table of geologic time spans presented here agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy. Evidence from radiometric dating indicates that Earth is about 4.54 billion years old. The geology or deep time of Earth’s past has been organized into various units according to events which took place in each period. Different spans of time on the GTS are usually delimited by changes in the composition of strata which correspond to them, indicating major geological or paleontological events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous–Paleogene extinction event, which marked the demise of the non-avian dinosaurs and many other groups of life. Older time spans which predate the reliable fossil record (before the Proterozoic Eon) are defined by the absolute age. Geologists have divided Earth's history into a series of time intervals. These time intervals are not equal in length like the hours in a day. Instead the time intervals are variable in length. This is because geologic time is divided using significant events in the history of the Earth.



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Fig. 10. Geological Time Scale 1. Eons Eons are the largest intervals of geologic time and are hundreds of millions of years in duration. In the time scale above you can see the Phanerozoic Eon is the most recent eon and began more than 500 million years ago. 2. Eras Eons are divided into smaller time intervals known as eras. In the time scale above you can see that the Phanerozoic is divided into three eras: Cenozoic, Mesozoic and Paleozoic. Very significant events in Earth's history are used to determine the boundaries of the eras. 3. Periods Eras are subdivided into periods. The events that bound the periods are wide-spread in their extent but are not as significant as those which bound the eras. In the time scale above you can see that the Paleozoic is subdivided into



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the Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician and Cambrian periods. 4. Epochs Finer subdivisions of time are possible and the periods of the Cenozoic are frequently subdivided into epochs. Subdivision of periods into epochs can be done only for the most recent portion of the geologic time scale. This is because older rocks have been buried deeply, intensely deformed and severely modified by long-term earth processes. As a result, the history contained within these rocks can not be as clearly interpreted. D. CATATROPHISM AND UNIFORMITARIANISM 1. The Theory of Catastrophism Catastrophism is the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. This was in contrast to uniformitarianism (sometimes described as gradualism), in which slow incremental changes, such as erosion, created all the Earth's geological features. Uniformitarianism held that the present is the key to the past, and that all things continued as they were from the indefinite past. Since the early disputes, a more inclusive and integrated view of geologic events has developed, in which the scientific consensus accepts that there were some catastrophic events in the geologic past, but these were explicable as extreme examples of natural processes which can occur. Catastrophism held that geological epochs had ended with violent and sudden natural catastrophes such as great floods and the rapid formation of major mountain chains. Plants and animals living in the parts of the world where such events occurred were killed off, being replaced abruptly by the new forms whose fossils defined the geological strata. Some catastrophists attempted to relate at least one such change to the Biblical account of Noah's flood. The leading scientific proponent of catastrophism in the early nineteenth century was the French anatomist and paleontologist Georges



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Cuvier. His motivation was to explain the patterns of extinction and faunal succession that he and others were observing in the fossil record. While he did speculate that the catastrophe responsible for the most recent extinctions in Eurasia might have been the result of the inundation of low-lying areas by the sea, he did not make any reference to Noah's flood. Nor did he ever make any reference to divine creation as the mechanism by which repopulation occurred following the extinction event. In fact Cuvier, influenced by the ideas of the Enlightenment and the intellectual climate of the French revolution, avoided religious or metaphysical speculation in his scientific writings. Cuvier also believed that the stratigraphic record indicated that there had been several of these revolutions, which he viewed as recurring natural events, amid long intervals of stability during the history of life on earth. This led him to believe the Earth was several million years old. 2. The Theory of Uniformitarianism Uniformitarianism is one of the most important unifying concepts in the geosciences. This concept developed in the late 1700s, suggests that catastrophic processes were not responsible for the landforms that existed on the Earth's surface. This idea was diametrically opposed to the ideas of that time period which were based on a biblical interpretation of the history of the Earth. Instead, the theory of uniformitarianism suggested that the landscape developed over long periods of time through a variety of slow geologic and geomorphic processes. The term uniformitarianism was first used in 1832 by William Whewell, a University of Cambridge scholar, to present an alternative explanation for the origin of the Earth. The prevailing view at that time was that the Earth was created through supernatural means and had been affected by a series of catastrophic events such as the biblical Flood. This theory is called catastrophism. The ideas behind uniformitarianism originated with the work of Scottish geologist James Hutton. In 1785, Hutton presented at the meetings of 20



the Royal Society of Edinburgh that the Earth had a long history and that this history could be interpreted in terms of processes currently observed. For example, he suggested that deep soil profiles were formed by the weathering of bedrock over thousands of years. He also suggested that supernatural theories were not needed to explain the geologic history of the Earth.



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CHAPTER III PALEONTOLOGY A. FOSSILS Fossils ") are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record. The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa (phylogeny) are some of the most important functions of the science of paleontology. Such a preserved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 years. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest, chemical fossils from the Archaean Eon, up to 3.48 billion years old, or even older, 4.1 billion years old, according to a 2015 study. The observation that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils. Like extant organisms, fossils vary in size from microscopic, even single bacterial cells one micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils. Finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals; these are known as chemofossils or biosignatures. 22



B. INVERTEBRATES FOSSILS Invertebrates are the multicellular animals without backbone. There are species of Crustaceans, Mollusca, Brachiopods, and etc. Invertebrates animals is live in almost all environment from the terrestrial to deep water. When it comes to the fossil record, soft-bodied and minuscule invertebrates— such as hydras, jellies, flatworms, hairworms, nematodes, ribbon worms, rotifers and roundworms -- are infrequently fossilized. As a result, paleontologists and other fossil hunters must often rely on trace fossils, microfossils, or chemofossil residue when scouting for these prehistoric creatures. Hard-bodied and large invertebrates are much-more commonly preserved; typically as sizeable macrofossils. These invertebrates are more frequently preserved because their hard parts—for example, shell, armor, plates, tests, exoskeleton, jaws or teeth -- are composed of silica (silicon dioxide), calcite or aragonite (both forms of calcium carbonate), chitin (a protein often infused with tricalcium phosphate), or keratin (an even-more complex protein), rather than the vertebrate bone (hydroxyapatite) or cartilage of fishes and land-dwelling tetrapods. The chitinous jaws of annelids (such as the marine scolecodonts) are sometimes preserved as fossils; while many arthropods and inarticulate brachiopods have easily fossilized hard parts of calcite, chitin, or keratin. The most common and often-found macrofossils are the very hard calcareous shells of articulate brachiopods (that is, the everyday "lampshells") and of mollusks (such as the omnipresent clams, snails, mussels and oysters). On the other hand, non-shelly slugs and non-tubiferous worms (for instance, earthworms) have only occasionally been preserved due to their lack of hard parts.



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C. FOSSIL PRESERVATION 1. Unaltered remains This does not mean the organism is unchanged, but that the original material of the organism has not been changed to another substance. The fossil may have lost water, or color, or the proteins of the soft tissue may have degraded. a. Unaltered



hard



and



soft



parts:



mummification,



freezing,



encasement in amber (fossilized tree sap). Very very rare, usually only very young fossils. b. Unaltered hard parts: teeth and very recent shells, bone or shell encased in petroleum or in petroleum-containing sediments. 2. Altered remains a. Permineralization: pore spaces within the fossil are filled with mineral, usually silica. Petrified wood, bone. b. Recrystallization: original mineral has recrystallized, either to different crystal system (aragonite to calcite) or by crystals growing. The original fine structure of the fossil is lost. c. Replacement: original mineral has been dissolved away and replaced by a different mineral. Usually the original mineral was aragonite or calcite, and it has been replaced by silica (in oxidizing and acidic conditions) or pyrite (in reducing conditions, in the absence of oxygen). Under some conditions, replacement happens on an atom-by-atom basis, and the fine structure of the fossil is preserved in the new mineral. Recognizing replacement requires that you first be able to recognize what mineral you are looking at, and then that you know what the original skeletal material was. See "Skeletal Materials" below. d. Carbonization: the soft parts of the organism were compressed and heated, driving off all the volatiles (H, N, O). A carbon film is left behind. Most common in plants, soft-bodied organisms, organisms with phosphate skeletons, organisms with chitin skeletons, and sometimes fish (under the right environmental conditions). 24



3. Impressions Sometimes an organism will leave an imprint in sediment. If that imprint is either rapidly buried or left undisturbed during slow burial, it can be lithified and become a fossil. We call shallow imprints impressions (common for leaves and flat shells). Deeper imprints are called molds. If a mold later fills with sediment or minerals, it will form a copy of the original fossil called a cast. 4. Traces Trace fossils are other kinds of evidence that an organism existed. Trace fossils include tracks, trails and footprints; burrows and other dwellings; tools; coprolites (fossilized excrement); and chemical fossils, which is chemical evidence of the existence of an organism. One of the most common but least useful kinds of trace fossils is bioturbation, evidence that organisms have churned through sediment. Bioturbation is recognized by the complete lack of sedimentary structures such as laminations and cross-beds, or by chaotic structures within the sediment. Unfortunately, it is usually impossible to tie bioturbation to any specific organism. D. FOSSIL AND EVOLUTION Fossils provide a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history. For instance, in 1998, scientists found a fossil showing an animal at the transition from sea creature to land creature. This tetrapod had a hand-like fin, confirming a prediction of evolutionary biology. Though the fossil record does not include every plant and animal that ever lived, it provides substantial evidence for the common descent of life via evolution.



The fossil record is a



remarkable gift for the study of nature. 1. Evidence of Gradual Change Organisms have changed significantly over time. In rocks more than 1 billion years old, only fossils of single-celled organisms are found. 25



Moving to rocks that are about 550 million years old, fossils of simple, multicellular animals can be found. At 500 million years ago, ancient fish without jawbones surface; and at 400 million years ago, fish with jaws are found. Gradually, new animals appear: amphibians at 350 million years ago, reptiles at 300 million years ago, mammals at 230 million years ago, and birds at 150 million years ago.1 As the rocks become more and more recent, the fossils look increasingly like the animals we observe today. 2. The Transition to Land: Sea Creatures to Land Animals Fossils of land animals, or tetrapods, first appear in rocks that are about 370 million years old. In older rocks, only sea creatures are found. But in 1998, scientists found a fossilized fin, 370 million years old, with eight digits similar to the five fingers humans have on their hands. 3. From Reptiles to Mammals Mammals first appeared in the fossil record about 230 million years ago, nearly 70 million years after reptiles first appeared. One group of reptiles, the cynodonts, first appeared about 260 million years ago and became increasingly mammal-like in more recent fossils—circa 245 million years ago. Scientists found a species of cynodonts, dating to just before the emergence of mammals, that had a double jaw hinge like that of a mammal. A pair of bones found in even earlier cynodont fossils seems to have transitioned slowly into the ear. No other fossils have been found that share a similar structure to the transitional cynodonts and date back before the time of mammals. Likewise, soon after mammals appeared, these cynodonts became extinct. This timing implies that the cynodont fossils record the transition from reptiles to mammals. 4. Transitional Forms: Few and Far Between Transitional forms occur just when one might expect to see a change from one body type to another. However, a common objection is that few transitional fossils have been discovered; thus many lineages cannot be traced smoothly. 26



There are several reason for these gaps in the fossil record. First, fossilization is a very rare event. Plus, transitional species tend to appear in small populations, where rapid changes in the environment can provide a stronger evolutionary drive. Finally, because fossilization itself is a rare event, smaller populations are sure to produce fewer fossils. The fact that transitional species have been found at all is remarkable, and it offers further support of gradual, evolutionary change. E. THE LAW OF FAUNAL SUCCESSION



Fig. 11. Faunal Succession The principle of faunal succession, also known as the law of faunal succession, is based on the observation that sedimentary rock strata contain fossilized flora and fauna, and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances. A fossilized Neanderthal bone will never be found in the same stratum as a fossilized Megalosaurus, for example, because neanderthals and megalosaurs lived during different geological periods, separated by many millions of years. This allows for strata to be identified and dated by the fossils found within. This principle, which received its name from the English geologist William Smith, is of great importance in determining the relative age of rocks and strata. The



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fossil content of rocks together with the law of superposition helps to determine the time sequence in which sedimentary rocks were laid down. Evolution explains the observed faunal and floral succession preserved in rocks. Faunal succession was documented by Smith in England during the first decade of the 19th century, and concurrently in France by Cuvier (with the assistance of the mineralogist Alexandre Brongniart). Archaic biological features and organisms are succeeded in the fossil record by more modern versions. For instance, paleontologists investigating the evolution of birds predicted that feathers would first be seen in primitive forms on flightless predecessor organisms such as feathered dinosaurs. This is precisely what has been discovered in the fossil record: simple feathers, incapable of supporting flight, are succeeded by increasingly large and complex feathers. F. NATURAL SELECTION Charles Darwin's theory of evolution is a theory of evolution based on natural selection theory, which was first proposed by Charles Darwin in his book "On the Origin of Species" or "Origin of Species" published in 1859. The theory of natural selection has the concept that a species that successfully adapt well will survive, while that can not adapt will become extinct. Darwin’s process of natural selection has four components, that is : 



Variation.



Organisms (within populations) exhibit individual variation in



appearance and behavior. These variations may involve body size, hair color, facial markings, voice properties, or number of offspring. On the other hand, some traits show little to no variation among individuals—for example, 



number of eyes in vertebrates. Inheritance. Some traits are consistently passed on from parent to offspring. Such traits are heritable, whereas other traits are strongly influenced by environmental conditions and show weak heritability.



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



High rate of population growth. Most populations have more offspring each year than local resources can support leading to a struggle for resources. Each







generation experiences substantial mortality. Differential survival and reproduction. Individuals possessing traits well suited for the struggle for local resources will contribute more offspring to the next generation. From one generation to the next, the struggle for resources (what Darwin



called the “struggle for existence”) will favor individuals with some variations over others and thereby change the frequency of traits within the population. This process is natural selection. The traits that confer an advantage to those individuals who leave more offspring are called adaptations. In order for natural selection to operate on a trait, the trait must possess heritable variation and must confer an advantage in the competition for resources. If one of these requirements does not occur, then the trait does not experience natural selection.



(We now know that such traits may change by other evolutionary



mechanisms that have been discovered since Darwin’s time.) Natural selection operates by comparative advantage, not an absolute standard of design. “…as natural selection acts by competition for resources, it adapts the inhabitants of each country only in relation to the degree of perfection of their associates” (Charles Darwin, On the Origin of Species, 1859). G. EVOLUTION Evolution is change in the heritable traits of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organisation, including the levels of species, individual organisms, and molecules. All life on Earth shares a common ancestor known as the last universal ancestor, which lived approximately 3.5–3.8 billion years ago, although a study in 2015 found "remains of biotic life" from 4.1 billion years ago in ancient rocks in



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Western Australia. According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe." Repeated formation of new species (speciation), change within species (anagenesis), and loss of species (extinction) throughout the evolutionary history of life on Earth are demonstrated by shared sets of morphological and biochemical traits, including shared DNA sequences. These shared traits are more similar among species that share a more recent common ancestor, and can be used to reconstruct a biological "tree of life" based on evolutionary relationships (phylogenetics), using both existing species and fossils. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, to fossilized multicellular organisms. Existing patterns of biodiversity have been shaped both by speciation and by extinction. More than 99 percent of all species that ever lived on Earth are estimated to be extinct. Estimates of Earth's current species range from 10 to 14 million, of which about 1.2 million have been documented. In the mid-19th century, Charles Darwin formulated the scientific theory of evolution by natural selection, published in his book On the Origin of Species (1859). Evolution by natural selection is a process demonstrated by the observation that more offspring are produced than can possibly survive, along with three facts about populations: 



Traits vary among individuals with respect to morphology, physiology, and







behaviour (phenotypic variation), Different traits confer different rates of survival and reproduction (differential







fitness), and Traits can be passed from generation to generation (heritability of fitness). Thus, in successive generations members of a population are replaced by progeny of parents better adapted to survive and reproduce in the biophysical environment in which natural selection takes place. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are seemingly fitted for the functional roles they perform.



Natural



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selection is the only known cause of adaptation but not the only known cause of evolution. Other, nonadaptive causes of microevolution include mutation and genetic drift. H. DARWIN’S LAWS Darwin’s laws of evolution entails the following fundamental ideas. The first three ideas were already under discussion among earlier and contemporaneous naturalists working on the “species problem” as Darwin began his research. Darwin’s original contributions were the mechanism of natural selection and copious amounts of evidence for evolutionary change from many sources. He also provided thoughtful explanations of the consequences of evolution for our understanding of the history of life and modern biological diversity. 1. Species (populations of interbreeding organisms) change over time and space. The representatives of species living today differ from those that lived in the recent past, and populations in different geographic regions today differ slightly in form or behavior. These differences extend into the fossil record, which provides ample support for this claim. 2. All organisms share common ancestors with other organisms. Over time, populations may divide into different species, which share a common ancestral population. Far enough back in time, any pair of organisms shares a common ancestor.



For example, humans shared a common



ancestor with chimpanzees about eight million years ago, with whales about 60 million years ago, and with kangaroos over 100 million years ago.



Shared ancestry explains the similarities of organisms that are



classified together: their similarities reflect the inheritance of traits from a common ancestor. 3. Evolutionary change is gradual and slow in Darwin’s view. This claim was supported by the long episodes of gradual change in organisms in the fossil record and the fact that no naturalist had observed the sudden



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appearance of a new species in Darwin’s time. Since then, biologists and paleontologists have documented a broad spectrum of slow to rapid rates of evolutionary change within lineages. I. DINOSAURS EXTINCTION Perhaps the most notable event of the Cretaceous was its conclusion. About 65 million years ago the second greatest mass extinction in Earth history occurred, resulting in the loss of the dinosaurs as well as nearly 50% of all the world’s species. Though not nearly as severe as the end-Permian mass extinction, the end-Cretaceous extinction is the most famous mass extinction in Earth history. Other great animals also went extinct at that time, including flying reptiles (pterosaurs) and the last mosasaurs and plesiosaurs. Many mollusks, including rudistid and inoceramid clams, ammonites, and belemnites, also became extinct, as did many species of microscopic marine plankton. Terrestrial plants also suffered a major extinction at this time; in some regions up to 60% of latest Cretaceous plant species were absent in the subsequent Paleocene. Terrestrial insects also suffered a high level of extinction, especially those that were highly specialized to feed on one or a few types of plants. In fact, the level of insect herbivory—both generalized and specialized—did not recover to latest Cretaceous levels until the Paleocene-Eocene boundary, approximately 9 million years later. In spite of the severity of extinctions at the end of the Cretaceous, many types of animals and plants survived and gave rise to new groups of organisms in the Paleocene. The asteroid would have hit with the force of 100,000 billion tons of TNT. This would have generated an earthquake one thousand times greater than the largest ever recorded, with winds of over 400 kph. A massive fireball would have boiled nearby seas, destroying everything for thousands of kilometers. Forests throughout most of North America and some of South America would have been flattened by the shock wave. Evidence of a giant tsunami has been found around the Gulf of Mexico



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and Caribbean, as well as in Spain and Brazil. It may have had an effect as far away as New Zealand. Map showing asteroid impact in Gulf of Mexico Despite the enormity of the destruction from the initial impact, the dinosaurs and their contemporaries might have survived and eventually recovered, but the subsequent long-term effects of the blast were even more deadly. Ninety thousand cubic kilometers of debris would have been blasted into the atmosphere, some reaching into space only to re-enter at high speeds. This could have heated the atmosphere sufficiently to ignite global forest fires. While the heavier pieces of ejecta settled back down on Earth, fine dust particles would have remained in the atmosphere and significantly blocked sunlight, causing an effect called an “impact winter”. There is much debate about the duration and severity of the impact winter following the K/T impact, but the darkness and cold temperatures might have reduced photosynthesis and collapsed food chains globally. The amount of carbon and sulfur contained in the rock at the impact site would have aggravated these devastating effects. As much as 100 billion tons of sulfur and 10 trillion tons of carbon would have been vaporized by the impact and blown into the atmosphere. The resulting sulfate aerosols would have stayed in the atmosphere for several years; the resulting carbon dioxide would have stayed airborne for several hundred years. Initially the sulfate aerosols would have contributed to global cooling by blocking out the sun, before precipitating as acid rain. After the dust and sulfates settled out and ended the cooling, global warming would have begun. The carbon dioxide levels, being two to three times normal, would have caused extreme greenhouse conditions, raising global temperatures by as much as 10°C. Although some life forms may have survived the years of darkness and freezing temperatures, many surely died out in the subsequent centuries of heat. Regardless of what caused the disappearance of the dinosaurs, the mass extinction at the end of the Cretaceous led the way for the rapid rise to dominance of new groups of organisms during the following time period, the Paleocene. In particular, Paleocene



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mammals would spread and evolve into the many ecological niches left open by the extinction of the dinosaurs. J. KT- BOUNDARY Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band. It defines the end of the Mesozoic Era, and is usually estimated at around 66 Ma (million years ago), with more specific radioisotope dating yielding an age of 66.043 ± 0.011 Ma. K is the traditional abbreviation for the Cretaceous Period, and Pg is the abbreviation for the Paleogene Period. The boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period of the Cenozoic Era. The boundary is associated with the Cretaceous–Paleogene extinction event, a mass extinction which is considered to be the demise of the non-avian dinosaurs in addition to a majority of the world's Mesozoic species. 1. The common ground a. There was global climatic change; the environment changed from a warm, mild one in the Mesozoic to a cooler, more varied one in the Cenozoic. The cause of this climate change, and the speed at which it proceeded, are the major concerns of both schools of thought. b. As well as a permanent global climatic change, there is evidence that there were less lasting changes at the end of the Cretaceous period. These changes may have been the result of a massive terrestrial disturbance, which threw up soot into the air, causing short term acid rain, emission of poisonous gases, and cooling (similar to a nuclear winter). Long term consequences would have been a global greenhouse effect (warming and reduced sunlight). c. Many organisms; both marine and terrestrial, vertebrate and invertebrate; went extinct. The reason for this extinction was probably this climate change.



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d. At or near the K-T boundary in several places around the globe, we have a thin layer of clay with an unusually high iridium (a rare metal similar to platinum) content. This may be evidence for the dust cloud in above. 2. The "intrinsic gradualists" Those scientists falling into this category believe that the ultimate cause of the K-T extinction was intrinsic; meaning of an Earthly nature; and gradual, taking some time to occur (several million years). Two main hypotheses exist today: a. Volcanism: We are quite certain that the end of the Cretaceous period that there was increased volcanic activity. Over a period of several million years, this increased volcanism could have created enough dust and soot to block out sunlight; producing the climatic change. In India during the Late Cretaceous, huge volcanic eruptions were spewing forth floods of lava which can be seen today at the K-T boundary (these ruptures in the Earth's surface are called the Deccan traps). The chemical composition of the lava rocks in India shows that they originated in the Earth's mantle, which is also relatively rich in iridium. This richness would explain the iridium layer. b. Plate Tectonics: Major changes in the organization of the continental plates (continental drift) were occurring at the K-T boundary. The oceans (especially the Interior Seaway in North America) were experiencing a regression; they were receding from the land. A less mild climate would have been the result, and this would have taken a long time. Large scale tectonic events did occur in the Mesozoic several times, and no extinction events have been conclusively associated with them yet. 3. The "extrinsic catastrophists" This side of the controversy holds that the ultimate cause of the K-T extinction was extrinsic, meaning of an extraterrestrial nature, and catastrophic, meaning fairly sudden and punctuated. The main hypothesis was 35



proposed in 1980 by (among others) Luis and Walter Alvarez of the University of California at Berkeley. 4. The Alvarez HypothesisT The original hypothesis is the basis for several subsequent variations on the theme that a large extraterrestrial object collided with the Earth, its impact throwing up enough dust to cause the climatic change. The iridium layer is what prompted the Alvarez team to blame an asteroid impact for the extinction — asteroids and similar extraterrestrial bodies are higher in iridium content than the Earth's crust, so they figured that the iridium layer must be composed of the dust from the vaporized meteor. No crater was found, but it was assumed that one existed that was about 65 million years old and 100 kilometers (about 65 miles) in diameter. Later research found a likely candidate for the crater at Chicxulub, on the Yucatan Peninsula of Mexico. Other evidence was also reported: the presence of shocked quartz in the rocks of the K-T boundary (indicating the passage of a shock wave so powerful that it actually rearranged the crystal structure of quartz grains), glassy spheres that looked like impact ejecta (molten rock that solidified into droplets when cooled), and a soot layer was found in many areas (evidence for widespread forest fires). The likelihood that massive hurricanes and firestorms would have raged across the Earth was also hypothesized, adding to the destructive power of the catastrophe. To reconcile the hypothesis with gradual data, it was suggested that rather than one impact, several impacts (of comets or meteors) could have occurred over a period of many years. Some evidence supported this — a hint of periodicity of mass extinctions in the fossil record was reported; mass extinctions seemed to occur roughly every 26 million years. Astronomers theorized that the Oort cloud of comets could cross the path of our solar system every 26 million years, and would possibly rain comets on our planet for a few million years. The existence of a tenth, as-yet unseen planet — or Nemesis, the twin star to our sun — both with large orbits were also 36



contemplated. To date, no reliable evidence for periodicity or Nemesis-type celestial bodies has been found, but this does not render the hypothesis obsolete; it is accepted that any large extraterrestrial body impacting the Earth's surface could and would produce climatic changes similar to those thought to have occurred around the K-T boundary.



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CHAPTER IV PLATE TECTONIC AND GEOSINCLIN A. GEOSYNCLINE THEORY DEVELOPMENT The development of Geosyncline theory is began of the theory of Hall: sedimentation very dense then led to subsidence, and the axis of the trough will be a range of mountains. The existence of subsidence is then produces the folded layers, but the multiplicity is not the cause of the increase in the thickness of sediment into the mountains. In addition, the sediment thickness above the trough / deepest basin resulted in the movement of materials subcrustal under the trough. The material moves laterally beneath sedimentary basins and foreland - his, so that the region rose. Naming Geosyncline introduced by Dana (1873), which is the process in which sediment accumulates a decline crust (Geosynclinal). In essence, the theory advanced by the Dana added a theory introduced by Hall. During the collapse of a large folding Geosyncline driven by lateral pressure, will form a series of large folding (synclinorium). Geosyncline decline to a depth of 35000 or 40000 feet, which means a mobile rock mass (thick or plastic), 7 mi and a maximum depth of more than 100 miles laterally, pushed aside. After that, the main part of moving to the east, and caused a trail bordered by the sea on the east side, which is then raised as a geantyclinal parallel with the subsidence troughs. Geantyclinal arc height may depend on how far the plastic rocks can move eastward. Then the floor Geosyncline become weaker due to isogeotherms, and this leads to weakening of sediment folding Geosyncline and childbirth mountain ranges. Theory Dana - Hall stating that mountain range is the birth Geosyncline based on two main opinions: 1. Determination of the location of the mountain ranges that will be formed based on the accumulation of sediment in a Geosyncline. 2. Mountains become vulnerable in the process is relatively short, for bedding folded and faulted. 38



According to L. De Launay (1921), Geosyncline is an important long zone where deposits bathyal continuously deposited up to a thickness, which run simultaneously deepening the accumulation. In the process, there are a few additions to the theory Hall – Dana : 1. Volcanism and intrusion during growth Geosyncline parent 2. Isostatic control for folding due to appression sediment Geosyncline 3. Metamorphism resulting from conditions Geosyncline and the events that followed the folding 4. Tthe intrusion of batholiths, syntectonic and epitectonic, and the relationship between intrusion batolith and folding succession of events that consists of a large-scale orogenesa revolution 5. Metal deposition is a result of successive cycles of volcanic activity during the revolution orogenesa. B. PLATE TECTONIC THEORY DEVELOPMENT In 1912 Alfred Wegener (1880-1930) noticed the same thing and proposed that the continents were once compressed into a single protocontinent which he called Pangaea (meaning "all lands"), and over time they have drifted apart into their current distribution. He believed that Pangaea was intact until the late Carboniferous period, about 300 million years ago, when it began to break up and drift apart. However, Wegener's hypothesis lacked a geological mechanism to explain how the continents could drift across the earths surface as he proposed. Searching for evidence to further develop his theory of continental drift, Wegener came across a paleontological paper suggesting that a land bridge had once connected Africa with Brazil. This proposed land bridge was an attempt to explain the well known paleontological observation that the same fossilized plants and animals from the same time period were found in South America and Africa. The same was true for fossils found in Europe and North America, and Madagascar and India. Many of these organisms could not have traveled across the vast oceans that currently exist. Wegener's drift theory seemed more plausible than land bridges connecting all 39



of the continents. But that in itself was not enough to support his idea. Another observation favoring continental drift was the presence of evidence for continental glaciation in the Pensylvanian period. Striae left by the scraping of glaciers over the land surface indicated that Africa and South America had been close together at the time of this ancient ice age. The same scraping patterns can be found along the coasts of South America and South Africa. Wegener eventually proposed a mechanism for continental drift that focused on his assertion that the rotation of the earth created a centrifugal force towards the equator.



He believed that Pangaea originated near the south pole and that the



centrifugal force of the planet caused the protocontinent to break apart and the resultant continents to drift towards the equator. He called this the "pole-fleeing force". This idea was quickly rejected by the scientific community primarily because the actual forces generated by the rotation of the earth were calculated to be insufficient to move continents. Wegener also tried to explain the westward drift of the Americas by invoking the gravitational forces of the sun and the moon, this idea was also quickly rejected. Wegener's inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories. Not until the 1960's did Holmes' idea receive any attention. Greater understanding of the ocean floor and the discoveries of features like mid-oceanic ridges, geomagnetic anomalies parallel to the mid-oceanic ridges, and the association of island arcs and oceanic trenches occurring together and near the continental margins, suggested convection might indeed be at work. These discoveries and more led Harry Hess (1962) and R.Deitz (1961) to publish similar hypotheses based on mantle convection currents, now known as "sea floor spreading". This idea was basically the same as that proposed by Holmes over 30 years earlier, but now there was much more evidence to further develop and support the idea. To learn more about the current theories which describe the mechanisms behind continental drift go to the "Plate Tectonics: The Mechanism" page. 40



C. PLATE MOVEMENT



Fig. 12. Plate Movement The tectonic plates of the earth is not stationary, but moves relative with the speed of 1 to 10 cm per year. The movement of the earth's crustal plates that collide with each other will form the subduction zone and cause the forces acting both horizontally and vertically, which will form the folds of the mountains, volcanoes track or magmatic, fracturing the rock, and the lines of tectonic earthquakes and the formation of a particular region. Moreover, that will also form various types of deposition of sedimentary basins such as trench, fore arc basin, back arc basin, and basin between the mountains. It is generally accepted that tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere. Dissipation of heat from the mantle is acknowledged to be the original source of the energy required to drive plate tectonics through convection or large scale upwelling and doming. The current view, though still a matter of some debate, asserts that as a consequence, a powerful source of plate motion is generated due to the excess density of the oceanic lithosphere sinking in subduction zones. When the new crust forms at



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mid-ocean ridges, this oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age as it conductively cools and thickens. The greater density of old lithosphere relative to the underlying asthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving force for plate movement. The weakness of the asthenosphere allows the tectonic plates to move easily towards a subduction zone. Although subduction is thought to be the strongest force driving plate motions, it cannot be the only force since there are plates such as the North American Plate which are moving, yet are nowhere being subducted. The same is true for the enormous Eurasian Plate. The sources of plate motion are a matter of intensive research and discussion among scientists. One of the main points is that the kinematic pattern of the movement itself should be separated clearly from the possible geodynamic mechanism that is invoked as the driving force of the observed movement, as some patterns may be explained by more than one mechanism. In short, the driving forces advocated at the moment can be divided into three categories based on the relationship to the movement: mantle dynamics related, gravity related (mostly secondary forces). Three types of plate boundaries exist, with a fourth, mixed type, characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are: 1. Transform boundaries (Conservative) occur where two lithospheric plates slide, or perhaps more accurately, grind past each other along transform faults, where plates are neither created nor destroyed. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer). Transform faults occur across a spreading center. Strong earthquakes can occur along a fault. The San Andreas Fault in California is an example of a transform boundary exhibiting dextral motion. 2. Divergent boundaries (Constructive) occur where two plates slide apart from each other. At zones of ocean-to-ocean rifting, divergent boundaries form by seafloor spreading, allowing for the formation of new ocean basin. As the 42



continent splits, the ridge forms at the spreading center, the ocean basin expands, and finally, the plate area increases causing many small volcanoes and/or shallow earthquakes. At zones of continent-to-continent rifting, divergent boundaries may cause new ocean basin to form as the continent splits, spreads, the central rift collapses, and ocean fills the basin. Active zones of Mid-ocean ridges (e.g., Mid-Atlantic Ridge and East Pacific Rise), and continent-to-continent rifting (such as Africa's East African Rift and Valley, Red Sea) are examples of divergent boundaries. 3. Convergent boundaries (Destructive) (or active margins) occur where two plates slide toward each other to form either a subduction zone (one plate moving underneath the other) or a continental collision. At zones of ocean-tocontinent subduction (e.g. the Andes mountain range in South America, and the Cascade Mountains in Western United States), the dense oceanic lithosphere plunges beneath the less dense continent. Earthquakes then trace the path of the downward-moving plate as it descends into asthenosphere, a trench forms, and as the subducted plate partially melts, magma rises to form continental volcanoes. At zones of ocean-to-ocean subduction (e.g. Aleutian islands, Mariana islands, and the Japanese island arc), older, cooler, denser crust slips beneath less dense crust. This causes earthquakes and a deep trench to form in an arc shape. The upper mantle of the subducted plate then heats and magma rises to form curving chains of volcanic islands. Deep marine trenches are typically associated with subduction zones, and the basins that develop along the active boundary are often called "foreland basins". The subducting slab contains many hydrous minerals which release their water on heating. This water then causes the mantle to melt, producing volcanism. Closure of ocean basins can occur at continent-to-continent boundaries (e.g., Himalayas and Alps): collision between masses of granitic continental lithosphere; neither mass is subducted; plate edges are compressed, folded, uplifted. 43



4. Plate boundary zones occur where the effects of the interactions are unclear, and the boundaries, usually occurring along a broad belt, are not well defined and may show various types of movements in different episodes.



Fig. 13. Plate Movement Type D. BASIN AND PLATE TETONIC 1. Plate Interactions In plate tectonic theory, composite continents are assembled by crustal collisions that occur when the consumption of oceanic lithosphere beneath arc-trench systems results in the closure of an oceanic basin. The arrival of a continental block at a subduction zone where the intervening oceanic lithosphere was consumed, will thus throttle subduction, and the position of the previous subduction zone will be taken by a crustal suture belt marking the line of tectonic juxtaposition of the two continental blocks involved in the crustal collision. All plate interactions that involve construction of new lithosphere or consumption of old lithosphere as a result of large horizontal motions of plates, involve significant vertical motions of the lithosphere. There are three basic causes of subsidence or uplift as a result of plate interactions:  Changes in crustal thickness  Thermal expansion or contraction of the lithosphere  Broad flexure of plates of the lithosphere in response to local tectonic or sedimentary loading.



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From a kinetic point of view, there are three kinds of plate junctures, analogous to the three classes of faults as defined by relative displacements: a. Divergent plate junctures (analogous to normal faults) A separation of two plates (sea-floor spreading) occurs and causes rupture of the intact old lithosphere, which in turn results in intercontinental rifting when an incipient rift crosses a continental block. The rate of spreading may average several centimeters per year and might produce over geologic time the continental drift that represents the separation of Africa and South America and the associated growth of the Atlantic Ocean. The plates diverge or move relatively apart and result in seafloor spreading, in which magmatic material from the underlying lithosphere wells up in between to form linear lava ridges parallel, linear “mid-ocean ridges” which are found in the Atlantic, Pacific, and Indian Oceans. b. Transform plate junctures (analogous to strike-dip faults) One plate slides laterally past the other along a transform or deep fault, without accretion or consumption. However, hybrid plate boundaries also occur in some areas, as in obliqueslip faults, where some component of extensional or contractional motion occurs along a transform, and hence the two terms transtension and transpression are used to describe the interaction. In accordance with the transform movements of the plates, the mid-ocean ridges in the Atlantic and Pacific Oceans, which run roughly north/south, are broken into a series of segments, each about 200 miles long, together with their related offsets, at the points of which are “transform fault zones,” formed roughly at right angles to the mid-ocean ridges, and projecting above the deep ocean floors; these become earthquake and volcano zones. c. Convergent plate junctures (analogous to thrust faults) 45



When two oceanic plates collide, one plate is thrust at an angle beneath the other, and dives down into the mantle where it is partially destroyed by heat. Convergent junctures are sites of plate consumption where oceanic lithosphere formed previously at a divergent plate juncture, descends into the mantle. Part of the slab continues to sink to a depth of about 700 km, where it comes to rest; the part which rises to merge with the upper plate is converted to low-density magma. Hobson (1975) discussed the convergence of plates according to a different approach, depending on whether oceanic- or continentaltype plates are involved.  A coastal mountain range is formed along the leading edge of the continental plate, when it is advancing towards and 



overriding a relatively stationary oceanic plate. Island arcs and subduction zone trenches are formed when an oceanic plate is advancing and passing beneath a







relatively stationary continental plate. Major mountain ranges are formed when two continentaltype plates slowly converge, as a result of the squeezing of the sediments carried on the underthrust plate (e.g., the Himalayas in India).



2. Development of Sedimentary Basins Plate tectonics theory is generally related to lateral and vertical motions of plates that form sedimentary basins. A sedimentary basin develops as an accumulated prism of strata, resulting either from subsidence of the basin floor, or from uplift of confining basin margins. Each basin has its own unique history connected to a particular sequence and combination of plate interactions and depositional conditions. During



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basin evolution, the stratigraphic fill of the basin took place because of the activity of the depositional systems. Folded and faulted structures within the basin were formed because of either tectonic or sedimentary evolution. Extensional deformation usually produces normal faults and tilted blocks, whereas contractional deformation produces folds and thrust faults. Plate movements have lately been considered to result from the presence of “hot spots,” which represent a number of thermal centers, and are fixed in the upper mantle, from which “plumes” of hot material rise intermittently to burn holes in the overlying crust. Consequently, the continental plates are pushed away from these “hot spots” by the creation of new ocean floor; and when the movement of the lithosphere above the plume occurs by the process of sea-floor spreading, a “plume scar” is left on the crust in the form of a line of volcanic cones.



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E. MID OCEANIC RIDGE Mid-Ocean Ridge is an underwater mountain system formed by plate tectonics. It consists of various mountains linked in chains, typically having a valley known as a rift running along its spine. This type of oceanic mountain ridge is characteristic of what is known as an oceanic spreading center, which is responsible for seafloor spreading. The production of new seafloor results from mantle upwelling in response to plate spreading; this isentropic upwelling solid mantle material eventually exceeds the solidus and melts. The buoyant melt rises as magma at a linear weakness in the oceanic crust, and emerges as lava, creating new crust upon cooling. A mid-ocean ridge demarcates the boundary between two tectonic plates, and consequently is termed a divergent plate boundary.



Fig. 14. Mid Oceanic Ridge Mid-ocean ridges are geologically active, with new magma constantly emerging onto the ocean floor and into the crust at and near rifts along the ridge axes. The crystallized magma forms new crust of basalt (known as MORB for mid-ocean ridge basalt) and gabbro. The rocks making up the crust below the seafloor are youngest at the axis of the ridge and age with increasing distance from that axis. New magma of basalt



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composition emerges at and near the axis because of decompression melting in the underlying Earth's mantle. The oceanic crust is made up of rocks much younger than the Earth itself. Most oceanic crust in the ocean basins is less than 200 million years old. The crust is in a constant state of "renewal" at the ocean ridges. Moving away from the mid-ocean ridge, ocean depth progressively increases; the greatest depths are in ocean trenches. As the oceanic crust moves away from the ridge axis, the peridotite in the underlying mantle cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere. Slow spreading ridges like the Mid-Atlantic Ridge (MAR) generally have large, wide rift valleys, sometimes as wide as 10–20 km (6.2–12.4 mi), and very rugged terrain at the ridge crest that can have relief of up to a 1,000 m (3,300 ft). By contrast, fast spreading ridges like the East Pacific Rise (EPR) are narrow, sharp incisions surrounded by generally flat topography that slopes away from the ridge over many hundreds of miles. The overall shape of ridges results from Pratt isostacy: close to the ridge axis there is hot, low-density mantle supporting the oceanic crust. As the oceanic plates cool, away from the ridge axes, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens and the density increases. Thus older seafloor is underlain by denser material and 'sits' lower. The width of the ridge is hence a function of spreading rate - slow ridges like the MAR have spread much less far than faster ridges like the EPR for the same amount of cooling and consequent bathymetric drop-off. There are two processes, ridge-push and slab pull, thought to be responsible for the spreading seen at mid-ocean ridges, and there is some uncertainty as to which is dominant. Ridge-push occurs when the growing bulk of the ridge pushes the rest of the tectonic plate away from the ridge, often towards a subduction zone. At the subduction zone, "slab-pull" comes into effect. This is simply the weight of the



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tectonic plate being subducted (pulled) below the overlying plate dragging the rest of the plate along behind it. F. SEISMIC ZONE A seismic zone is a region in which the rate of seismic activity remains fairly consistent. This may mean that seismic activity is incredibly rare, or that it is extremely common. Some people often use the term “seismic zone” to talk about an area with an increased risk of seismic activity, while others prefer to talk about “seismic hazard zones” when discussing areas where seismic activity is more frequent. There are studies that show that much of the damage done in earthquakes is, perhaps, due rather to the velocity of the back and forth movements of the earth, rather than to the ground acceleration. However, the mean and peak ground accelerations do have much to do with the intensity of damage a building may have to withstand. Consequently, engineers and designers rely a great deal on the measure of the peak ground acceleration, as compared to gravity, to determine how strong an earthquake force a new building may have to withstand. Instruments called accelerographs measure ground acceleration against the value of gravity (acceleration in g/10). These values are gathered from all parts of the nation to create a seismic-risk map, which is used by engineers and builders when designing earthquake-resistant structures for different parts of the country. Attenuation is another important detail that is factored into plotting a seismicrisk map. Attenuation is, basically, how far earthquakes’ waves are felt, and what is the duration of the earthquakes. This is very different in various parts of the nation. Example, in the values on the seismic-risk map are that in seismic zone 4, we have a one in ten chance that an earthquake with an active peak acceleration level of 0.4g (4/10 the acceleration of gravity) will occur within the next fifty years.



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CHAPTER V THE ORIGIN OF THE EARTH A. THE ORIGIN OF THE UNIVERSE Big Bang model, widely held theory of the evolution of the universe. Its essential feature is the emergence of the universe from a state of extremely high temperature and density—the so-called big bang that occurred 13.8 billion years ago. Although this type of universe was proposed by Russian mathematician Aleksandr Friedmann and Belgian astronomer Georges Lemaître in the 1920s, the modern version was developed by Russian-born American physicist George Gamow and colleagues in the 1940s. The big-bang model is based on two assumptions. The first is that Albert Einstein’s general theory of relativity correctly describes the gravitational interaction of all matter. The second assumption, called the cosmological principle, states that an observer’s view of the universe depends neither on the direction in which he looks nor on his location. This principle applies only to the large-scale properties of the universe, but it does imply that the universe has no edge, so that the big-bang origin occurred not at a particular point in space but rather throughout space at the same time. These two assumptions make it possible to calculate the history of the cosmos after a certain epoch called the Planck time. Scientists have yet to determine what prevailed before Planck time. According to the big-bang model, the universe expanded rapidly from a highly compressed primordial state, which resulted in a significant decrease in density and temperature. Soon afterward, the dominance of matter over antimatter (as observed today) may have been established by processes that also predict proton decay. During this stage many types of elementary particles may have been present. After a few seconds, the universe cooled enough to allow the formation of certain nuclei. The theory predicts that definite amounts of hydrogen, helium, and lithium were produced. Their abundances agree with what is observed today. About one 51



million years later the universe was sufficiently cool for atoms to form. The radiation that also filled the universe was then free to travel through space. This remnant of the early universe is the cosmic microwave background radiation—the “three degree” (actually 2.728 K) background radiation discovered in 1965 by American physicists Arno A. Penzias and Robert W. Wilson. In addition to accounting for the presence of ordinary matter and radiation, the model predicts that the present universe should also be filled with neutrinos, fundamental particles with no mass or electric charge. The possibility exists that other relics from the early universe may eventually be discovered. B. THE SOLAR SYSTEM



Fig. 15. The Solar System The Solar System comprises the Sun and the planetary system that orbits it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets and small Solar System bodies such as comets and asteroids. Of those that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with most of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn,



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are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called ices, such as water, ammonia and methane. All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic. The Solar System also contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations are several dozen to possibly tens of thousands of objects large enough to have been rounded by their own gravity. Such objects are categorized as dwarf planets. Identified dwarf planets include the asteroid Ceres and the transNeptunian objects Pluto and Eris. In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust, freely travel between regions. Six of the planets, at least three of the dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of interstellar wind; it extends out to the edge of the scattered disc. The Oort cloud, which is believed to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way.



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The following is the member of solar system : 1. Sun The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses) produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium, making it a main-sequence star. This releases an enormous amount of energy, mostly radiated into space as electromagnetic radiation peaking in visible light. The Sun is a G2-type main-sequence star. Hotter main-sequence stars are more luminous. The Sun's temperature is intermediate between that of the hottest stars and that of the coolest stars. Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, make up 85% of the stars in the Milky Way. The Sun is a population I star; it has a higher abundance of elements heavier than hydrogen and helium ("metals" in astronomical parlance) than the older population II stars. Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the Universe could be enriched with these atoms. The oldest stars contain few metals, whereas stars born later have more. This high metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets form from the accretion of "metals". 2. Mercury Mercury (0.4 AU from the Sun) is the closest planet to the Sun and the smallest planet in the Solar System (0.055 Earth masses). Mercury has no natural satellites; besides impact craters, its only known geological features are lobed ridges or rupes that were probably produced by a period of contraction early in its history. Mercury's very tenuous atmosphere consists of atoms blasted off its surface by the solar wind. Its relatively large iron core and thin mantle have not yet been adequately explained.



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Hypotheses include that its outer layers were stripped off by a giant impact; or, that it was prevented from fully accreting by the young Sun's energy. 3. Venus Venus (0.7 AU from the Sun) is close in size to Earth (0.815 Earth masses) and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere, and evidence of internal geological activity. It is much drier than Earth, and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C (752°F), most likely due to the amount of greenhouse gases in the atmosphere. No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is being replenished by volcanic eruptions. 4. Earth Earth (1 AU from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist. Its liquid hydrosphere is unique among the terrestrial planets, and it is the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen. It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System. 5. Mars Mars (1.5 AU from the Sun) is smaller than Earth and Venus (0.107 Earth masses). It possesses an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (roughly 0.6% of that of Earth). Its surface, peppered with vast volcanoes, such as Olympus Mons, and rift valleys, such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago Its red colour comes from



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iron oxide (rust) in its soil. Mars has two tiny natural satellites (Deimos and Phobos) thought to be captured asteroids. 6. Asteroids Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of refractory rocky and metallic minerals, with some ice. They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), depending on different, somewhat arbitrary definitions. The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter. Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth. The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident. 7. Jupiter Jupiter (5.2 AU), at 318 Earth masses, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. Jupiter has 67 known satellites. The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating. Ganymede, the largest satellite in the Solar System, is larger than Mercury. 8. Saturn Saturn (9.5 AU), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less



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than a third as massive, at 95 Earth masses, making it the least dense planet in the Solar System. The rings of Saturn are made up of small ice and rock particles. Saturn has 62 confirmed satellites; two of which, Titan and Enceladus, show signs of geological activity, though they are largely made of ice. Titan, the second-largest moon in the Solar System, is larger than Mercury and the only satellite in the Solar System with a substantial atmosphere. 9. Uranus Uranus (19.2 AU), at 14 Earth masses, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other giant planets and radiates very little heat into space. Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel, and Miranda. 10. Neptune Neptune (30.1 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and hence more dense. It radiates more internal heat, but not as much as Jupiter or Saturn. Neptune has 14 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen. Triton is the only large satellite with a retrograde orbit. Neptune is accompanied in its orbit by several minor planets, termed Neptune trojans, that are in 1:1 resonance with it.



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C. EARTH CRUST COMPOSITION The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust occupies less than 1% of Earth's volume. The oceanic crust of the sheet is different from its continental crust. 



The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick and is composed







primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km (20 mi) to 50 km (30 mi) thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust. Both the continental and oceanic crust "float" on the mantle. Because the



continental crust is thicker, it extends both to greater elevations and greater depth than the oceanic crust. The slightly lower density of felsic continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, water runs off the continents and collects above the oceanic crust. Because of the change in velocity of seismic waves it is believed that beneath continents at a certain depth continental crust (sial) becomes close in its physical properties to oceanic crust (sima), and the transition zone is referred to as the Conrad discontinuity. The temperature of the crust increases with depth, reaching values typically in the range from about 200 °C (392 °F) to 400 °C (752 °F) at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere. Because of convection in the underlying plastic (although non58



molten) upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C (about 50 °F) for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust. The continental crust has an average composition similar to that of andesite. Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle. Although the continental crust comprises only about 0.6 weight percent of the silicate on Earth, it contains 20% to 70% of the incompatible elements. The following is diagram about the abundant element and mineral in the earth crust :



Fig. 16. The abundant element and mineral diagram D. GEOSYNCLINE Geosyncline, linear trough of subsidence of the Earth’s crust within which vast amounts of sediment accumulate. The filling of a geosyncline with thousands or tens of thousands of feet of sediment is accompanied in the late stages of deposition by folding, crumpling, and faulting of the deposits. Intrusion of crystalline igneous rock and regional uplift along the axis of the trough generally complete the history of a particular geosyncline, which is thus transformed to a belt of folded mountains. The concept of the geosyncline was introduced by the American geologist James Hall in



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1859. Most modern geologists regard the concept as obsolete and largely explain the development of linear troughs in terms of plate tectonics; the term geosyncline, however, remains in use.



Fig. 17. Geosyncline Geosynclines are divided into miogeosynclines and eugeosynclines, depending on the types of discernible rock strata of the mountain system. 



A miogeosyncline develops along a passive margin of a continent and is composed of sediments with limestones, sandstones and shales. The occurrences of limestones and well-sorted quartz sandstones indicate a







shallow-water formation. A eugeosyncline consists of rocks from deep marine environments. Eugeosynclinal rocks include thick sequences of greywackes, cherts, slates, tuffs and submarine lavas. The eugeosynclinal deposits are typically more deformed, metamorphosed, and intruded by small to large igneous plutons. Eugeosynclines often contain flysch typical of a continental-continental convergent boundary.. Aside from the parts or segments of a geosyncline, several types of mobile



zones have been recognized and named. Among the more common of these are the taphrogeosyncline, a depressed block of the Earth’s crust that is bounded by one or more high-angle faults and that serves as a site of sediment accumulation, and the paraliageosyncline, a deep geosyncline that passes into coastal plains along continental margins. E. PLATE TECTONIC



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Plate Tectonic is a theory that describes about Earth's lithosphere in the large scale. This theory has been built on the concept of continental drift. Lithosphere is the outermost layer of the earth, the lithosphere is divided into several sections which are often called plate tectonics. The Earth's lithosphere is composed of seven or eight major plates and many minor plates. Where the plates meet, their relative motion determines the type of boundary that is convergent, divergent, or transform. Tectonic plates are composed of oceanic lithosphere and continental lithosphere. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The following is an explanation of plate tectonics : 1. The Drift of the Continents



Fig. 18. Continental Drift The Earth surface looked very different 200 million years ago from its present appearance. In particular, the continents have changed because they sit on blocks of the lithosphere that are in horizontal motion with respect to each other, and indeed they continue to change because the horizontal motion continues.



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The present continents separated from two supercontinents called Laurasia and Gondwanaland through this process of plate tectonics. The two supercontinents may have once been united in a single supercontinent called Pangaea, though this is less certain. 2. The Origin of Plate Tectonics



Fig. 19. The origin of plate tectonics The continents drift slowly but that they drift at all is remarkable. The following figure illustrates the structure of the first 100-200 kilometers of the Earth's interior, and provides an answer to this question. The crust is thin, varying from a few tens of kilometers thick beneath the continents to to less than 10 km thick beneath the many of the oceans. The crust and upper mantle together constitute the lithosphere, which is typically 50-100 km thick and is broken into large plates. The aesthenosphere is kept plastic largely through heat generated by radioactive decay. The material that is decaying is primarily radioactive 62



isotopes of light elements like aluminum and magnesium. This heat source is small on an absolute scale. Nevertheless, because of the insulating properties of the Earth's rocks this is sufficient to keep the aesthenosphere plastic in consistency. 3. Convection Currents



Fig. 20. Convection Currents Very slow convection currents flow in this plastic layer, and these currents provide horizontal forces on the plates of the lithosphere much as convection in a pan of boiling water causes a piece of cork on the surface of the water to be pushed sideways. The differentiation is crucial to plate tectonics on the Earth, because it is responsible for producing an interior that can support tectonic motion.



F. PLUME THEORY In 1971, geophysicist W. Jason Morgan proposed the hypothesis of mantle plumes. In this hypothesis, convection in the mantle transports heat from the core to 63



the Earth's surface in thermal diapirs. In this concept, two largely independent convective processes occur in the mantle: the broad convective flow associated with plate tectonics, which is driven primarily by the sinking of cold plates of lithosphere back into the mantle asthenosphere, and mantle plumes, which carry heat upward in narrow, rising columns, driven by heat exchange across the core-mantle boundary. The latter type of convection is postulated to be independent of plate motions. The sizes and occurrence of mushroom mantle plumes can be predicted easily by transient instability theory developed by Tan and Thorpe. The theory predicts mushroom mantle plumes of about 2000 km diameter with a critical time of about 830 Myr for a core mantle heat flux of 20 mW/m2, while the cycle time is about 2 Gyr. The number of mantle plumes is predicted to be about 17. The narrow vertical pipe, or conduit, postulated to connect the plume head to the core-mantle boundary, is viewed as providing a continuous supply of magma to a fixed location, often referred to as a "hot spot". As the overlying tectonic plate (lithosphere) moves over this "hot spot", the eruption of magma from the fixed conduit onto the surface is expected to form a chain of volcanoes that parallels plate motion. The Hawaiian Islands chain in the Pacific Ocean is the type example. Interestingly, it has recently been discovered that the volcanic locus of this chain has not been fixed over time, and it thus joined the club of the many type examples that do not exhibit the key characteristic originally proposed. The chemical and isotopic composition of basalts found at "hot spots" differs subtly from mid-ocean-ridge basalts. This geochemical signature arises from the mixing of near-surface materials such as subducted slabs and continental sediments, in the mantle source. There are two competing interpretations for this. In the context of mantle plumes, the near-surface material is postulated to have been transported down to the core-mantle boundary by subducting slabs, and to have been transported back up to the surface by plumes. In the context of the Plate hypothesis, subducted material is mostly re-circulated in the shallow mantle and tapped from there by volcanoes. 64



The processing of oceanic crust, lithosphere, and sediment through a subduction zone decouples the water-soluble trace elements (e.g., K, Rb, Th) from the immobile trace elements (e.g., Ti, Nb, Ta), concentrating the immobile elements in the oceanic slab (the water-soluble elements are added to the crust in island arc volcanoes). Seismic tomography shows that subducted oceanic slabs sink as far as the bottom of the mantle transition zone at 650 km depth. Subduction to greater depths is less certain, but there is evidence that they may sink to mid-lower-mantle depths at about 1,500 km depth. The source of mantle plumes, is postulated to be the core-mantle boundary at 3,000 km depth. Because there is little material transport across the core-mantle boundary, heat transfer must occur by conduction, with adiabatic gradients above and below this boundary. The core-mantle boundary is a strong thermal (temperature) discontinuity. The temperature of the core is approximately 1,000 degrees Celsius higher than that of the overlying mantle. Plumes are postulated to rise as the base of the mantle becomes hotter and more buoyant. Plumes are postulated to rise through the mantle and begin to partially melt on reaching shallow depths in the asthenosphere by decompression melting. This would create large volumes of magma. The plume hypothesis postulates that this melt rises to the surface and erupts to form "hot spots". G. BIG BANG THEORY 1. History and Development Big Bang Theory English astronomer Fred Hoyle is credited with coining the term "Big Bang" during a 1949 BBC radio broadcast. It is popularly reported that Hoyle, who favored an alternative "steady state" cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models. The Big Bang theory developed from observations of the structure of the universe and from theoretical considerations. In 1912 Vesto Slipher 65



measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way. Ten years later, Alexander Friedmann, a Russian cosmologist and mathematician, derived the Friedmann equations from Albert Einstein's equations of general relativity, showing that the universe might be expanding in contrast to the static universe model advocated by Einstein at that time. In 1924 Edwin Hubble's measurement of the great distance to the nearest spiral nebulae showed that these systems were indeed other galaxies. Independently deriving Friedmann's equations in 1927, Georges Lemaître, a Belgian physicist and Roman Catholic priest, proposed that the inferred recession of the nebulae was due to the expansion of the universe. Significant progress in Big Bang cosmology have been made since the late 1990s as a result of advances in telescope technology as well as the analysis of data from satellites such as COBE, the Hubble Space Telescope and WMAP. Cosmologists now have fairly precise and accurate measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the universe appears to be accelerating. 2. Big Bang Theory



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Fig. 21 Big Bang The Big Bang theory is the prevailing cosmological model for the universe from the earliest known periods through its subsequent largescale evolution. The model accounts for the fact that the universe expanded from a very high density and high temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure and Hubble's Law. If the known laws of physics are extrapolated beyond where they are valid, there is a singularity. Modern measurements place this moment at approximately 13.8 billion years ago, which is thus considered the age of the universe. After the initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies. Since Georges Lemaître first noted, in 1927, that an expanding universe might be traced back in time to an originating single point, scientists have built on his idea of cosmic expansion. While the scientific community was once divided between supporters of two different expanding universe theories, the Big Bang and the Steady State theory, accumulated empirical evidence provides strong support for the former. In 1929, from analysis of galactic redshifts, Edwin Hubble concluded that galaxies are drifting apart, important observational evidence consistent with the hypothesis of an expanding universe. In 1965, the cosmic microwave background radiation was discovered, which was crucial evidence in favor of the Big Bang model, since that theory predicted the existence of background radiation throughout the universe before it was discovered. More recently, measurements of the redshifts of supernovae indicate that the expansion of the universe is accelerating, an observation



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attributed to dark energy's existence. The known physical laws of nature can be used to calculate the characteristics of the universe in detail back in time to an initial state of extreme density and temperature. Hubble observed that the distances to faraway galaxies were strongly correlated with their redshifts. This was interpreted to mean that all distant galaxies and clusters are receding away from our vantage point with an apparent velocity proportional to their distance: that is, the farther they are, the faster they move away from us, regardless of direction. Assuming the Copernican principle (that the Earth is not the center of the universe), the only remaining interpretation is that all observable regions of the universe are receding from all others. Since we know that the distance between galaxies increases today, it must mean that in the past galaxies were closer together. The continuous expansion of the universe implies that the universe was denser and hotter in the past. Large particle accelerators can replicate the conditions that prevailed after the early moments of the universe, resulting in confirmation and refinement of the details of the Big Bang model. However, these accelerators can only probe so far into high energy regimes. Consequently, the state of the universe in the earliest instants of the Big Bang expansion is still poorly understood and an area of open investigation and indeed, speculation. The first subatomic particles included protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed. The majority of atoms produced by the Big Bang were hydrogen, along with helium and traces of lithium. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies, and the heavier elements were synthesized either within stars or during supernovae.



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The Big Bang theory offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure, and Hubble's Law. The framework for the Big Bang model relies on Albert Einstein's theory of general relativity and on simplifying assumptions such as homogeneity and isotropy of space. The governing equations were formulated by Alexander Friedmann, and similar solutions were worked on by Willem de Sitter. Since then, astrophysicists have incorporated observational and theoretical additions into the Big Bang model, and its parametrization as the Lambda-CDM model serves as the framework for current investigations of theoretical cosmology. The Lambda-CDM model is the standard model of Big Bang cosmology, the simplest model that provides a reasonably good account of various observations about the universe. 3. Chronology of Events Big Bang a. Singularity Extrapolation of the expansion of the universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This singularity signals the breakdown of general relativity and thus, all the laws of physics. How closely this can be extrapolated toward the singularity is debated—certainly no closer than the end of the Planck epoch. This singularity is sometimes called "the Big Bang", but the term can also refer to the early hot, dense phase itself, which can be considered the "birth" of our universe. Based on measurements of the expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background, the universe has an estimated age of 13.799 ± 0.021 billion years. The agreement of these three independent measurements strongly supports the ΛCDM model that describes in detail the contents of the universe. 69



b. Inflation and baryogenesis The earliest phases of the Big Bang are subject to much speculation. In the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures and was very rapidly expanding and cooling. Approximately 10−37 seconds into the expansion, a phase transition caused a cosmic inflation, during which the universe grew exponentially. After inflation stopped, the universe consisted of a quark–gluon plasma, as well as all other elementary particles. Temperatures were so high that the random motions of particles were at relativistic speeds, and particle–antiparticle pairs of all kinds were being continuously created and destroyed in collisions. At some point an unknown reaction called baryogenesis violated the conservation of baryon number, leading to a very small excess of quarks and leptons over antiquarks and antileptons—of the order of one part in 30 million. This resulted in the predominance of matter over antimatter in the present universe. c. Cooling The universe continued to decrease in density and fall in temperature, hence the typical energy of each particle was decreasing. Symmetry breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form. After about 10−11 seconds, the picture becomes less speculative, since particle energies drop to values that can be attained in particle physics experiments. At about 10−6 seconds, quarks and gluons combined to form baryons such as protons and neutrons. The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. The temperature was now no longer high enough to create new proton–antiproton pairs (similarly for neutrons–antineutrons), so a mass annihilation immediately followed, leaving just one in 1010 of 70



the original protons and neutrons, and none of their antiparticles. A similar process happened at about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the universe was dominated by photons (with a minor contribution from neutrinos). A few minutes into the expansion, when the temperature was about a billion (one thousand million; 109; SI prefix giga-) kelvin and the density was about that of air, neutrons combined with protons to form the universe's deuterium and helium nuclei in a process called Big Bang nucleosynthesis. Most protons remained uncombined as hydrogen nuclei. As the universe cooled, the rest mass energy density of matter came to gravitationally dominate that of the photon radiation. After about 379,000 years the electrons and nuclei combined into atoms (mostly hydrogen); hence the radiation decoupled from matter and continued through space largely unimpeded. This relic radiation is known as the cosmic microwave background radiation. The chemistry of life may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the universe was only 10–17 million years old. d. Structure formation Over a long period of time, the slightly denser regions of the nearly uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures observable today. The details of this process depend on the amount and type of matter in the universe. The four possible types of matter are known as cold dark matter, warm dark matter, hot dark matter, and baryonic matter. The best measurements available (from WMAP) show that the data is well-fit by a Lambda-CDM model in which dark matter is assumed to be cold 71



(warm dark matter is ruled out by early reionization), and is estimated to make up about 23% of the matter/energy of the universe, while baryonic matter makes up about 4.6%. In an "extended model" which includes hot dark matter in the form of neutrinos, then if the "physical baryon density" Ωbh2 is estimated at about 0.023 (this is different from the 'baryon density' Ωb expressed as a fraction of the total matter/energy density, which as noted above is about 0.046), and the corresponding cold dark matter density Ωch2 is about 0.11, the corresponding neutrino density Ωvh2 is estimated to be less than 0.0062. e. Cosmic acceleration Independent lines of evidence from Type Ia supernovae and the CMB imply that the universe today is dominated by a mysterious form of energy known as dark energy, which apparently permeates all of space. The observations suggest 73% of the total energy density of today's universe is in this form. When the universe was very young, it was likely infused with dark energy, but with less space and everything closer together, gravity predominated, and it was slowly braking the expansion. But eventually, after numerous billion years of expansion, the growing abundance of dark energy caused the expansion of the universe to slowly begin to accelerate. Dark energy in its simplest formulation takes the form of the cosmological constant term in Einstein's field equations of general relativity, but its composition and mechanism are unknown and, more generally, the details of its equation of state and relationship with the Standard Model of particle physics continue to be investigated both observationally and theoretically. All of this cosmic evolution after the inflationary epoch can be rigorously described and modelled by the ΛCDM model of cosmology, which uses the independent frameworks of quantum mechanics and 72



Einstein's General Relativity. There is no well-supported model describing the action prior to 10−15 seconds or so. Apparently a new unified theory of quantum gravitation is needed to break this barrier. Understanding this earliest of eras in the history of the universe is currently one of the greatest unsolved problems in physics.



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CHAPTER VI PRECAMBRIAN A. GENERAL INFORMATION Precambrian was a time before the Cambrian. Precambrian is the longest period in the geological time scale in which this period starts from the first time that the Earth was formed about 4.6 billion years ago to 542 million years ago. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and those fossils present (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks have been heavily metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata. It is thought that the Earth itself coalesced from material in orbit around the Sun roughly 4500 Ma, or 4.5 billion years ago (Ga), and may have been struck by a very large (Mars-sized) planetesimal shortly after it formed, splitting off material that formed the Moon (see Giant impact hypothesis). A stable crust was apparently in place by 4400 Ma, since zircon crystals from Western Australia have been dated at 4404 Ma. The term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names. It was briefly also called the Cryptozoic eon.



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B. DIVISION PRECAMBRIAN



Fig 22. Precambrian Timeline 1. Hadean Hadean Era began with the formation of the earth from dust and gas orbiting the Sun about 4.6 billion years ago. During this era the surface of the Earth was like popular visions about Hades: oceans of liquid rock, boiling sulfur, and impact craters everywhere! Volcanoes blast off all over the place, and the rain of rocks and asteroids from space never ends. It's hard to take a step without falling in a pool of lava or getting hit by a meteor! The air is hot, thick, steamy, and full of dust and crud. But you can't breathe it anyway: it's made of nothing but carbon dioxide and water vapor, with traces of nitrogen and smelly sulfur compounds! Any rocks that do form from cooling lavas are quickly buried under new lava flows or blasted to bits by yet another impact. Some people think that an asteroid as large as the planet Mars hit the Earth near the beginning of the Hadean era, completely smashing and melting the Earth and forming the Moon as part of the splash. No one has found any rocks on earth from this era. Only meteorites from space and moon rocks are this old. If any life formed on earth during this era, it was probably destroyed.



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Fig. 23. Earth in Hadean 2. Archean Archean ("Ancient" or "Primitive") Era begins about a billion years after the formation of the earth, and things have changed a lot. Mostly everything has cooled down. Most of the water vapor that was in the air has cooled and condensed to form a global ocean. Even most of the carbon dioxide is gone, having been chemically changed into limestone and deposited at the bottom of the ocean. The air is now mostly nitrogen, and the sky is filled with normal clouds and rain. The lava is also mostly cooled to form the ocean floor. The interior of the earth is still quite hot and active, as shown by the many erupting volcanoes. The volcanoes form lots of small islands in long chains. The islands are the only land surface. The continents have not formed yet. The islands are carried over the surface of the earth by the movement of rock deep in the earth's interior. (This movement results from the loss of heat from the deep interior and is called plate tectonics.) Occasionally the small islands collide with each other to form larger islands. Eventually these larger islands will collide to form the cores of the continents we know today. Thank goodness those pesky asteroids and meteorites are now mostly gone, so impact craters form only occasionally. Evidence of blue-green algae (actually



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simple bacteria) floating in the ocean. That's all there is! Just single-celled bacteria in the ocean. There is as yet no life on land. Life began in the ocean near the beginning of this era. The oldest known fossils - the remains of different types of bacteria - are in archean rocks about 3.5 billion years old.



Fig. 24. Earth in Archaean 3. Proterozoic Proterozoic ("Early Life") Era. Well, here we are about 700 million years ago, near the end of the longest time period in geologic history. It began about two billion years after the formation of the earth and lasted about another two billion years! So what has happened in all that time? Hmmmmm. There is a lot more land to be seen. In fact, there are two supercontinents, one visible across the equator on this side of the earth and another one on the other side. These huge masses of land formed by collisions of the many, many islands made by volcanoes during the Archean and most of the Proterozoic eras. The earth's interior has cooled some more, and there are fewer volcanoes than in the Archean. Even though the movements of the earth's surface we call Plate Tectonics are still very fast and continental collisions are frequent (every few hundred million years or so!), the centers or cores of the continents are now quite large and stable. In fact, geologists date the beginning of the Proterozoic Era by the age of the oldest continental rocks that have not been reheated or chemically altered. Life has not changed much during the last two



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billion years, but the few changes are significant. Life is still found only in the ocean, but somewhere around 1.7 billion years ago, single-celled creatures appeared that had a real nucleus. Another important change is about to happen: true multi-celled life is about to appear, some 30 million years before the end of the Proterozoic. These multi-celled creatures will have no hard parts like shells or teeth in their bodies, so their fossils will be hard to find. The atmosphere is about the same, mostly nitrogen, with a little water vapor and carbon dioxide. But what's this? Free oxygen released by the algae floating in the oceans is beginning to collect in the air. These single-celled plants have been producing oxygen for about two billion years, but up until now the oxygen has been combining chemically with iron and other elements to form great mineral deposits around the world. Paradoxically, this oxygen, which we must have to live, is poisonous to most of the life forms living on the Earth during the Proterozoic, so another great change in the types of life is about to occur. The earth at this time is also very cold, with huge, bluish glacial ice sheets visible across the supercontinent, even in the normally warm equatorial regions!



In fact, glaciers invaded Michigan at this time; this glaciation is



referred to as the Gowganda glaciation.



Fig. 25. Earth in Proterozoic C. EVIDENCE AND FOSSIL RECORD IN CAMBRIAN



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The earliest living organisms were microscopic bacteria, which show up in the fossil record as early as 3.4 billion years ago. As their numbers multiplied and supplies of their chemical fuel were eaten up, bacteria sought out an alternative energy source. New varieties began to harness the power of the sun through a biochemical process known as photosynthesis—a move that would ultimately lead to simple plants and which opened the planet up to animal life. Some three billion years ago the Earth's atmosphere was virtually devoid of oxygen. At about 2.4 billion years ago, oxygen was released from the seas as a byproduct of photosynthesis by cyanobacteria. Levels of the gas gradually climbed, reaching about one percent around two billion years ago. About 800 million years ago, oxygen levels reached about 21 percent and began to breathe life into more complex organisms. The oxygen-rich ozone layer was also established, shielding the Earth's surface from harmful solar radiation. The first multicelled animals appeared in the fossil record almost 600 million years ago. Known as the Ediacarans, these bizarre creatures bore little resemblance to modern life-forms. They grew on the seabed and lacked any obvious heads, mouths, or digestive organs. Fossils of the largest known among them, Dickinsonia, resemble a ribbed doormat. What happened to the mysterious Ediacarans isn't clear. They could be the ancestors of later animals, or they may have been completely erased by extinction. The earliest multicelled animals that survived the Precambrian fall into three main categories. The simplest of these soft-bodied creatures were sponges. Lacking organs or a nervous system, they lived by drawing water through their bodies and filtering out food particles. The cnidarians, which included sea anemones, corals, and jellyfish, had sac-like bodies and a simple digestive system with a mouth but no anus. They caught food using tentacles armed with microscopic stinging cells. The third group, the annelids, or segmented flatworms, had fluid-filled body cavities and breathed through their skins.



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It's thought the final stages of Precambrian time were marked by a prolonged global ice age. This may have led to widespread extinctions, mirroring the bleak endings to the geologic periods that followed.



Fig. 26. Cambrian Fossil Record



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CHAPTER VII PALEOZOIC



Fig. 27. Paleozoic Timeline Paleozoic is the era of the geological time scale in which this era starts from 542-251 million years ago. This era is divided into the following: A. CAMBRIAN The Cambrian Period is the first geological time period of the Paleozoic Era (the “time of ancient life”). This period lasted about 53 million years and marked a dramatic burst of evolutionary changes in life on Earth, known as the "Cambrian Explosion." Among the animals that evolved during this period were the chordates, animals with a dorsal nerve cord; hard-bodied brachiopods, which resembled clams; and arthropods, ancestors of spiders, insects and crustaceans.



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Though there is some scientific debate about what fossil strata should mark the beginning of the period, the International Geological Congress places the lower boundary of the period at 543 million years ago with the first appearance in the fossil record of worms that made horizontal burrows. The end of the Cambrian Period is marked by evidence in the fossil record of a mass extinction event about 490 million years ago. The Cambrian Period was followed by the Ordovician Period. The period gets its name from Cambria, the Roman name for Wales, where Adam Sedgwick, one of the pioneers of geology, studied rock strata. Charles Darwin was one of his students. (Sedgwick, however, never accepted Darwin's theory of evolution and natural selection.) 1. Climate of the Cambrian Period In the early Cambrian, Earth was generally cold but was gradually warming as the glaciers of the late Proterozoic Eon receded. Tectonic evidence suggests that the single supercontinent Rodinia broke apart and by the early to mid-Cambrian there were two continents. Gondwana, near the South Pole, was a supercontinent that later formed much of the land area of modern Africa, Australia, South America, Antarctica and parts of Asia. Laurentia, nearer the equator, was composed of landmasses that currently make up much of North America and part of Europe. Increased coastal area and flooding due to glacial retreat created more shallow sea environments. At this point, no life yet existed on land; all life was aquatic. Very early in the Cambrian the sea floor was covered by a “mat” of microbial life above a thick layer of oxygen-free mud. The first multicellular life forms had evolved in the late Proterozoic to “graze” on the microbes. These multicellular organisms were the first to show evidence of a bilateral body plan. These near-microscopic “worms” began to burrow, mixing and oxygenating the mud of the ocean floor. During this time, dissolved oxygen was increasing in the water because of the presence of



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cyanobacteria. The first animals to develop calcium carbonate exoskeletons built coral reefs. The middle of the Cambrian Period began with an extinction event. Many of the reef-building organisms died out, as well as the most primitive trilobites. One hypothesis suggests that this was due to a temporary depletion of oxygen caused by an upwelling of cooler water from deep ocean areas. This upwelling eventually resulted in a variety of marine environments ranging from the deep ocean to the shallow coastal zones. Scientists hypothesize that this increase in available ecological niches set the stage for the abrupt radiation in life forms commonly called the “Cambrian Explosion.” 2. Fossils of the Cambrian Period Scientists find some of the best specimens for the “evolutionary experiments” of the Cambrian Period in the fossil beds of the Sirius Passet formation in Greenland; Chenjiang, China; and the Burgess Shale of British Columbia. These formations are remarkable because the conditions of fossilization led to impressions of both hard and soft body parts and the most complete records of the varieties of organisms alive in the Cambrian Period. The Sirius Passet formation has fossils estimated to be from the early Cambrian Period. Arthropods are the most abundant, although the groups are not as diverse as those found in the later Burgess Shale formation. The Sirius Passet has the first fossil indications of complex predator/prey relationships. For example, Halkieria were slug-shaped animals with shell caps at either end. The rest of the body was covered in smaller armor plates over a soft snail-like “foot.” It is unclear whether they are more closely related to the annelids, such as modern-day earthworms and leeches, or are a primitive mollusk. Some specimens have been found in curled up defensive postures like modern pill bugs. Predator/prey



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relationships provide intensive selection pressures that lead to rapid speciation and evolutionary change. Burgess Shale fossils are from the late Cambrian. Diversity had increased dramatically. There are at least 12 species of trilobite in the Burgess Shale; whereas in the Sirius Passet, there are only two. It is clear that representatives of every animal phylum, excepting only the Bryozoa, existed by this time. 3. Subdivisions The Cambrian period follows the Ediacaran and is followed by the Ordovician period. The Cambrian is divided into four epochs or series and ten ages or stages. Currently only two series and five stages are named and have a GSSP. Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban, 541 ± 0.3 to 509 ± 1.7 mya), Middle Cambrian (St Davids or Albertan, 509 ± 0.3 to 497 ± 1.7 mya) and Furongian (497 ± 0.3 to 485.4 ± 1.7 mya; also known as Late Cambrian, Merioneth or Croixan). Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian. B. ORDOVICIAN The Ordovician Period lasted almost 45 million years, beginning 488.3 million years ago and ending 443.7 million years ago.* During this period, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern supercontinent Gondwana. Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater. The Ordovician is best known for its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More recently, tetrahedral spores 84



that are similar to those of primitive land plants have been found, suggesting that plants invaded the land at this time. From the Lower to Middle Ordovician, the Earth experienced a milder climate the weather was warm and the atmosphere contained a lot of moisture. However, when Gondwana finally settled on the South Pole during the Upper Ordovician, massive glaciers formed, causing shallow seas to drain and sea levels to drop. This likely caused the mass extinctions that characterize the end of the Ordovician in which 60% of all marine invertebrate genera and 25% of all families went extinct. 1. Life Ordovician strata are characterized by numerous and diverse trilobites and conodonts (phosphatic fossils with a tooth-like appearance) found in sequences of shale, limestone, dolostone, and sandstone. In addition, blastoids, bryozoans, corals, crinoids, as well as many kinds of brachiopods, snails, clams, and cephalopods appeared for the first time in the geologic record in tropical Ordovician environments. Remains of ostracoderms (jawless, armored fish) from Ordovician rocks comprise some of the oldest vertebrate fossils. Despite the appearance of coral fossils during this time, reef ecosystems continued to be dominated by algae and sponges, and in some cases by bryozoans. However, there apparently were also periods of complete reef collapse due to global disturbances. The major global patterns of life underwent tremendous change during the Ordovician. Shallow seas covering much of Gondwana became breeding grounds for new forms of trilobites. Many species of graptolites went extinct by the close of the period, but the first planktonic graptolites appeared. In the late Lower Ordovician, the diversity of conodonts decreased in the North Atlantic Realm, but new lineages appeared in other regions. Seven major conodont lineages went extinct, but were replaced by nine new lineages that resulted from a major evolutionary radiation. These lineages included many new and morphologically different taxa. Sea level transgression 85



persisted causing the drowning of almost the entire Gondwana craton. By this time, conodonts had reached their peak development. Although fragments of vertebrate bone and even some soft-bodied vertebrate relatives are now known from the Cambrian, the Ordovician is marked by the appearance of the oldest complete vertebrate fossils. These were jawless, armored fish informally called ostracoderms, but more correctly placed in the taxon Pteraspidomorphi. Typical Ordovician fish had large bony shields on the head, small, rod-shaped or platelike scales covering the tail, and a slitlike mouth at the anterior end of the animal. Such fossils come from nearshore marine strata of Ordovician age in Australia, South America, and western North America. Perhaps the most "groundbreaking" occurrence of the Ordovician was the colonization of the land. Remains of early terrestrial arthropods are known from this time, as are microfossils of the cells, cuticle, and spores of early land plants. 2. Stratigraphy The Ordovician was named by the British geologist Charles Lapworth in 1879. He took the name from an ancient Celtic tribe, the Ordovices, renowned for its resistance to Roman domination. For decades, the epochs and series of the Ordovician each had a type location in Britain, where their characteristic faunas could be found, but in recent years, the stratigraphy of the Ordovician has been completely reworked. Graptolites, extinct planktonic organisms, have been and still are used to correlate Ordovician strata. Particularly good examples of Ordovician sequences are found in China (Yangtze Gorge area, Hubei Province), Western Australia (Emanuel Formation, Canning Basin), Argentina (La Chilca Formation, San Juan Province), the United States (Bear River Range, Utah), and Canada (Survey Peak Formation, Alberta). Ordovician rocks over much of these areas are typified by a considerable thickness of lime and other carbonate rocks that accumulated in shallow subtidal and intertidal environments. Quartzites are



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also present. Rocks formed from sediments deposited on the margins of Ordovician shelves are commonly dark, organic-rich mudstones which bear the remains of graptolites and may have thin seams of iron sulfide. 3. Tectonics and paleoclimate During the Ordovician, most of the world's land — southern Europe, Africa, South America, Antarctica, and Australia — was collected together in the super-continent Gondwana. Throughout the Ordovician, Gondwana moved towards the South Pole where it finally came to rest by the end of the period. In the Lower Ordovician, North America roughly straddled the equator and almost all of that continent lay underwater. By the Middle Ordovician North America had shed its seas and a tectonic highland, roughly corresponding to the later Appalachian Mountains, formed along the eastern margin of the continent. Also at this time, western and central Europe were separated and located in the southern tropics; Europe shifted towards North America from higher to lower latitudes. During the Middle Ordovician, uplifts took place in most of the areas that had been under shallow shelf seas. These uplifts are seen as the precursor to glaciation. Also during the Middle Ordovician, latitudinal plate motions appear to have taken place, including the northward drift of the Baltoscandian Plate (northern Europe). Increased sea floor spreading accompanied by volcanic activity occurred in the early Middle Ordovician. Ocean currents changed as a result of lateral continental plate motions causing the opening of the Atlantic Ocean. Sea levels underwent regression and transgression globally. Because of sea level transgression, flooding of the Gondwana craton occurred as well as regional drowning which caused carbonate sedimentation to stop. During the Upper Ordovician, a major glaciation centered in Africa occurred resulting in a severe drop in sea level which drained nearly all craton platforms. This glaciation contributed to ecological disruption and mass extinctions. Nearly all conodonts disappeared in the North Atlantic Realm 87



while only certain lineages became extinct in the Midcontinental Realm. Some trilobites, echinoderms, brachiopods, bryozoans, graptolites, and chitinozoans also became extinct. The Atlantic Ocean closed as Europe moved towards North America. Climatic fluctuations were extreme as glaciation continued and became more extensive. Cold climates with floating marine ice developed as the maximum glaciation was reached. C. SILURIAN The Silurian (443.7 to 416.0 million years ago)* was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it. One result of these changes was the melting of large glacial formations. This contributed to a substantial rise in the levels of the major seas. The Silurian witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations. Coral reefs made their first appearance during this time, and the Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the first fish with jaws. It is also at this time that our first good evidence of life on land is preserved, such as relatives of spiders and centipedes, and also the earliest fossils of vascular plants. 1. Life The Silurian is a time when many biologically significant events occurred. In the oceans, there was a widespread radiation of crinoids, a continued proliferation and expansion of the brachiopods, and the oldest known fossils of coral reefs. As mentioned earlier, this time period also marks the wide and rapid spread of jawless fish, along with the important appearances of both the first known freshwater fish and the appearance of jawed fish. Other marine fossils commonly found throughout the Silurian record include trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks. 88



It is also in the Silurian that we find the first clear evidence of life on land. While it is possible that plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils (a group of fungi), as well as remains of the first arachnids and centipedes. Perhaps most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cooksonia, a collection of branching-stemmed plants which produced sporangia at their tips. None of these plants had leaves, and some appear to have lacked vascular tissue. Also from the Silurian of Australia comes a controversial fossil of Baragwanathia, a lycophyte. If such a complex plant with leaves and a fully-developed vascular system was present by this time, then surely plants must have been around already by the Ordovician. In any event, the Silurian was a time for important events in the history of evolution, including many "firsts," that would prove highly consequential for the future of life on Earth. 2. Stratigraphy The Silurian's stratigraphy is subdivided into four epochs (from oldest to youngest): the Llandovery, Wenlock, Ludlow, and Pridoli. Each epoch is distinguished from the others by the appearance of new species of graptolites. Graptolites are a group of extinct colonial, aquatic animals that put in their first appearance in the Cambrian Period and persisted into the early Carboniferous. The beginning of the Silurian (and the Llandovery) is marked by the appearance of Parakidograptus acuminatus, a species of graptolite. The Llandovery (443.7-428.2 million years ago*) preserves its fossils in shale, sandstone, and gray mudstone sediment. Its base (beginning) is 89



marked by the appearance of the graptolites Parakidograptus acuminatus and Akidograptus ascensus. The Llandoverian epoch is subdivided into the Rhuddanian, Aeronian, and Telychian stages. At the close of the Telychian stage, the appearance of Cyrtograptus centrifugus marks the start of the Wenlockian epoch (428.2 to 422.9 million years ago).* The fossils are found in siltstone and mudstone under limestone. Missing from the fossil record of the Wenlock was the conodont Pterospathodus amorphognathoides, present in earlier strata. This is an epoch with excellent preservations of brachiopod, coral, trilobite, clam, bryozoan, and crinoid fossils. The Wenlock is subdivided into the Sheinwoodian and Homerian stages. The Ludlow (422.9 to 418.7 million years ago)* consists of siltstone and limestone strata, marked by the appearance of Neodiversograptus nilssoni. There is an abundance of shelly animal fossils. The Gorstian and Ludfordian stages make up the Ludlow epoch. Platy limestone strata rich in cephalopods and bivalves characterize the Pridolian (418.7 to 416.0 million years ago),* the final epoch of the Silurian. It is marked by the appearance of the index fossil Monograptus parultimus, and also by two new species of chitinozoans (marine plankton), Urnochitina urna and Fungochitina kosovensis, which appear at the base or just above the base of the Pridoli. 3. Tectonics and paleoclimate Although there were no major periods of volcanism during the Silurian, the period is marked by major orogenic events in eastern North America and in northwestern Europe (the Caledonian Orogeny), resulting in the formation of the mountain chains there. The ocean basins between the regions known as Laurentia (North America and Greenland), Baltica (central and northern Europe and Scandinavia) and Avalonia (western Europe) closed substantially, continuing a geologic trend that had begun much earlier. The modern Philippine Islands were near the Arctic Circle,



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while Australia and Scandinavia resided in the tropics; South America and Africa were over the South Pole. While not characterized by dramatic tectonic activity, the Silurian world experienced gradual continental changes that would be the basis for greater global consequences in the future, such as those that created terrestrial ecosystems. A deglaciation and rise in sea levels created many new marine habitats, providing the framework for significant biological events in the evolution of life. Coral reefs, for example, made their first appearance in the fossil record during this time. The Silurian Period's condition of low continental elevations with a high global stand in sea level can be strongly distinguished from the present-day environment. This is a result of the flood of 65% of the shallow seas in North America during the Llandovery and Wenlock times. The shallow seas ranged from tropical to subtropical in climate. Coral mound reefs with associated carbonate sediments were common in the shallow seas. Due to reduced circulation during the Ludlow and Pridoli times, the process of deposition of evaporites (salts) was set in motion. Some of these deposits are found in northern Europe, Siberia, South China and Australia. D. DEVONIAN During the Devonian, two major animal groups colonized the land. The first tetrapods land-living vertebrates



appeared during the Devonian, as did the first



terrestrial arthropods, including wingless insects and the earliest arachnids. In the oceans, brachiopods flourished. Crinoids and other echinoderms, tabulate and rugose corals, and ammonites were also common. Many new kinds of fish appeared. During the Devonian, there were three major continental masses: North America and Europe sat together near the equator, with much of their current area covered by shallow seas. To the north lay a portion of modern Siberia. A composite



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continent of South America, Africa, Antarctica, India, and Australia dominated the southern hemisphere. 1. Life a. The Devonian seas The Devonian seas were dominated by brachiopods, such as the spiriferids, and by tabulate and rugose corals, which built large reefs in shallow waters. Encrusting red algae also contributed to reef building. In the Lower Devonian, ammonoids appeared, leaving us large limestone deposits from their shells. Bivalves, crinoid and blastoid echinoderms, graptolites, and trilobites were all present, though most groups of trilobites disappeared by the close of the Devonian. The Devonian is also notable for the rapid diversification in fish. Benthic, jawless, armored fish are common by the Lower Devonian. These early fish include a number of different groups. By the the Middle Devonian, placoderms, the first jawed fish, appear. Many of these grew to large sizes and were fearsome predators. Of the greatest interest to us is the rise of the first sarcopterygians, the lobe-finned fish, which eventually produced the first tetrapods just before the end of the Devonian. b. The Devonian landscape By the Devonian Period, colonization of the land was well underway. Before this time, there was no organic accumulation in the soils, resulting in soils with a reddish color. This is indicative of the underdeveloped landscape, probably colonized only by bacterial and algal mats. By the start of the Devonian, early terrestrial vegetation had begun to spread. These plants did not have roots or leaves like most plants today, and many had no vascular tissue at all. They probably spread vegetatively, rather than by spores or seeds, and did not grow much more than a few centimeters tall. These plants 92



included the now extinct zosterophylls and trimerophytes. The early fauna living among these plants were primarily arthropods: mites, trigonotarbids, wingless insects, and myriapods, though these early faunas are not well known. By the Late Devonian, lycophytes, sphenophytes, ferns, and progymnosperms had evolved. Most of these plants have true roots and leaves, and many grew quite tall. The progymnosperm Archaeopteris (see photo above) was a large tree with true wood. It was the oldest known tree until the 2007 identification of Wattieza in 2007. By the end of the Devonian, the first seed plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion." Along with this diversification in terrestrial vegetation structure, came a diversification of the arthropods. 2. Tectonics and paleoclimate Significant changes in the world's geography took place during the Devonian. During this period, the world's land was collected into two supercontinents, Gondwana and Euramerica. These vast landmasses lay relatively near each other in a single hemisphere, while a vast ocean covered the rest of the globe. These supercontinents were surrounded on all sides by subduction zones. With the development of the subduction zone between Gondwana and Euramerica, a major collision was set in motion that would bring the two together to form the single worldcontinent Pangea in the Permian. In addition to global patterns of change, many important regional activities also occurred. The continents of North America and Europe collided, resulting in massive granite intrusions and the raising of the Appalachian Mountains of eastern North America. Vigorous erosion of these newly uplifted mountains yielded great volumes of sediment, which were deposited in vast lowlands and shallow seas nearby. 93



Extensive reef building, producing some of the world's largest reef complexes, proceeded as stromatoporoids and corals appeared in increasing numbers. These were built in the equatorial seas between the continents. Large shallow seas in North America, central Asia, and Australia became basins in which great quantities of rock salt, gypsum, and other minerals precipitated. Near the end of the Devonian, a mass extinction event occurred. Glaciation and the lowering of the global sea level may have triggered this crisis, since the evidence suggests warm water marine species were most affected. Meteorite impacts have also been blamed for the mass extinction, or changes in atmospheric carbon dioxide. It is even conceivable that it was the evolution and spread of forests and the first plants with complex root systems that may have altered the global climate. Whatever the cause, it was about this time that the first vertebrates moved onto the land.



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E. CARBONIFEROUS The Carboniferous Period lasted from about 359.2 to 299 million years ago* during the late Paleozoic Era. The term "Carboniferous" comes from England, in reference to the rich deposits of coal that occur there. These deposits of coal occur throughout northern Europe, Asia, and midwestern and eastern North America. The term "Carboniferous" is used throughout the world to describe this period, although in the United States it has been separated into the Mississippian (early Carboniferous) and the Pennsylvanian (late Carboniferous) Subsystems. This division was established to distinguish the coal-bearing layers of the Pennsylvanian from the mostly limestone Mississippian, and is a result of differing stratigraphy on the different continents. The Mississippian and Pennsylvanian, in turn, are subdivided into a number of internationally recognized stages based on evolutionary successions of fossil groups . These stages are (from early to late) Tournaisian, Visean, and Serpukhovian for the Mississippian and Bashkirian, Moscovian, Kasimovian, and Gzhelian for the Pennsylvanian. 1. Life The beginning of the Carboniferous generally had a more uniform, tropical, and humid climate than exists today. Seasons if any were indistinct. These observations are based on comparisons between fossil and modern-day plant morphology. The Carboniferous plants resemble those that live in tropical and mildly temperate areas today. Many of them lack growth rings, which suggests a uniform climate. This uniformity in climate may have been the result of the large expanse of ocean that covered the entire surface of the globe, except for a localized section where Pangea, the massive supercontinent that existed during the late Paleozoic and early Triassic, was coming together. Shallow, warm, marine waters often flooded the continents. Attached filter feeders such as bryozoans, particularly fenestellids, were abundant in this environment, and the sea floor was dominated by brachiopods.



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Trilobites were increasingly scarce while foraminifers were abundant. The heavily armored fish from the Devonian became extinct, being replaced with more modern-looking fish fauna. Uplifting near the end of the Mississippian resulted in increased erosion, with an increase in the number of floodplains and deltas. The deltaic environment supported fewer corals, crinoids, blastoids, cryozoans, and bryzoans, which were abundant earlier in the Carboniferous. Freshwater clams made their first appearance, and there was an increase in gastropod, bony fish, and shark diversity. As the continents moved closer to forming Pangea, there was a net decrease in coastline, which in turn affected the diversity of marine life in those shallow continental waters. Two large ice sheets at the southern pole locked up large amounts of water as ice. With so much water taken out of the water cycle, sea levels dropped, leading to an increase in terrestrial habitat. Increases and decreases in glaciation during the Pennsylvanian resulted in sea level fluctuations that can be seen in the rocks as striped patterns of alternating shale and coal layers. The uplift of the continents caused a transition to a more terrestrial environment during the Pennsylvanian Subsystem, although swamp forests were widespread. In the swamp forests, seedless plants such as lycopsids flourished and were the primary source of carbon for the coal that is characteristic of the period. The lycopods underwent a major extinction event after a drying trend, most likely caused by increased glaciation, during the Pennsylvanian. Ferns and sphenopsids became more important later during the Carboniferous, and the earliest relatives of the conifers appeared. The first land snails appeared and insects with wings that can't fold back, such as dragonflies and mayflies, flourished and radiated. These insects, as well as millipedes, scorpions, and spiders became important in the ecosystem.



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A trend towards aridity and an increase in terrestrial habitat led to the increasing importance of the amniotic egg for reproduction. The earliest amniote fossil was the lizard-like Hylonomus, which was lightly built with deep, strong jaws and slender limbs. The basal tetrapods became more diverse during the Carboniferous. Predators with long snouts, short sprawling limbs and flattened heads such as temnospondyls, like Amphibiamus (above) appeared. Anthracosaurs — basal tetrapods and amniotes with deep skulls and a less sprawling body plan that afforded greater agility — appeared during the Carboniferous and were quickly followed by diapsids which divided into two groups: (1) the marine reptiles, lizards, and snakes, and (2) the archosaurs — crocodiles, dinosaurs, and birds. The synapsids also made their first appearance, and presumably the anapsids did as well, although the oldest fossils for that group are from the Lower Permian. 2. Stratigraphy The appearance or disappearance of fauna usually marks the boundaries between time periods. The Carboniferous is separated from the earlier Devonian by the appearance of the conodont Siphonodella sulcata or Siphondella duplicata. Conodonts are fossils that resemble the teeth or jaws of primitive eel- or hagfish-like fish. The Carboniferous-Permian boundary is distinguished by the appearance of the fusulinid foram Sphaeroschwagerina fusiformis in Europe and Pseudoschwagerina beedei in North America. Fusulinids are giants among protists and could reach a centimeter in length. They were abundant enough to form sizable deposits known as "rice rock" because of the resemblance between fusulinids and rice grains. The Mississippian Subsystem is differentiated from the Pennsylvanian by the appearance of the conodont Declinognathodus noduliferus, the ammonoid genus Homoceras, and the foraminifers Millerella pressa and Millerella marblensis, though these markers apply only to marine deposits. 97



The distinction between the Mississippian and Pennsylvanian subsystems may also be illustrated by a break in the flora due to transitional changes from a marine to a more terrestrial environment. The stratigraphy of the Mississippian is distinguished by shallowwater limestones. Some of these limestones are composed of parts of organisms, primarily the remains of crinoids that thrived in the shallow seas. Other limestones include lime mudstones, composed of the carbonate mud produced by green algae, and oolithic limestones, composed of calcium carbonate in concentric spheres produced by high wave energy. Also found in Mississippian strata, though not as common, are sandstones (sedimentary rock composed of quartz sand and cemented by silica or calcium carbonate) and siltstones (rock composed of hardened silt). F. PERMIAN The Permian period lasted from 299 to 251 million years ago and was the last period of the Paleozoic Era. The distinction between the Paleozoic and the Mesozoic is made at the end of the Permian in recognition of the largest mass extinction recorded in the history of life on Earth. It affected many groups of organisms in many different environments, but it affected marine communities the most by far, causing the extinction of most of the marine invertebrates of the time. Some groups survived the Permian mass extinction in greatly diminished numbers, but they never again reached the ecological dominance they once had, clearing the way for another group of sea life. On land, a relatively smaller extinction of diapsids and synapsids cleared the way for other forms to dominate, and led to what has been called the "Age of Dinosaurs." Also, the great forests of fern-like plants shifted to gymnosperms, plants with their offspring enclosed within seeds. Modern conifers, the most familiar gymnosperms of today, first appear in the fossil record of the Permian. The Permian was a time of great changes and life on Earth was never the same again. The global geography of the Permian included massive areas of land and water. By the beginning of the Permian, the motion of the Earth's crustal plates had 98



brought much of the total land together, fused in a supercontinent known as Pangea. Many of the continents of today in somewhat intact form met in Pangea (only Asia was broken up at the time), which stretched from the northern to the southern pole. Most of the rest of the surface area of the Earth was occupied by a corresponding single ocean, known as Panthalassa, with a smaller sea to the east of Pangea known as Tethys. Models indicate that the interior regions of this vast continent were probably dry, with great seasonal fluctuations due to the lack of a moderating effect provided by nearby bodies of water. Only portions of this interior region received rainfall throughout the year. There is little known about the Panthalassic Ocean itself. There are indications that the climate of the Earth shifted during the Permian, with decreasing glaciation as the interiors of continents became drier. Until the later 1990s, there was little consensus on the order of strata in the late Permian. Since the upper strata of various Permian locations tend to be relatively fossil deficient, correlation using index fossils has been difficult. Correlation was attempted using fossils that were in some cases native only to the local regions where they were found and older work was based on assumptions that have changed in more recent years. Older classifications relied on the Ural Mountains stratigraphy. In 1994, Jin et al. proposed a worldwide stratigraphy of the Permian Period made up of four series/epochs: the Uralian, the Chihsian, the Guadalupian, and the Lopingian. In the early 2000s, work by Jin and others resulted in the stratigraphy currently accepted by the International Commission on Stratigraphy. The current stratigraphy divides the Permian into three series or epochs: the Cisuralian (299 to 270.6 mya), Guadalupian (270.6 to 260.4 mya), and Lopingian (260.4 to 251 mya).* Find out more about how these periods of time are defined. Permian shales, sandstones, siltstones, limestones, sands, marls, and dolostones were deposited as a result of sea-level fluctuations. These fluctuation cycles can be seen in 99



the rock layers. Relatively few sites lend themselves to direct radioactive dating, so the age of intermediate strata is often estimated. Permian fossils that have been used as index fossils include brachiopods, ammonoids, fusilinids, conodonts, and other marine invertebrates, and some genera occur within such specific time frames that strata are named for them and permit stratigraphic identification through the presence or absence of specified fossils.



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CHAPTER VIII MESOZOIC



Fig. 28. Mesozoic Timeline A. TRIASSIC In many ways, the Triassic was a time of transition. It was at this time that the world-continent of Pangaea existed, altering global climate and ocean circulation. The Triassic also follows the largest extinction event in the history of life, and so is a time when the survivors of that event spread and recolonized. The organisms of the Triassic can be considered to belong to one of three groups: holdovers from the Permo-Triassic extinction, new groups which flourished briefly, and new groups which went on to dominate the Mesozoic world. The holdovers included the lycophytes, glossopterids, and dicynodonts. While those that went on to dominate the Mesozoic world include modern conifers, cycadeoids, and the dinosaurs. The Triassic period was a transition from the Paleozoic Era to the Mesozoic. It is situated between the end of the Permian period and the beginning of 101



the Jurassic, lasting from 254 mya to 206 mya. As with almost any other period of the Earth's history, the Triassic had a unique climate and biota indigenous to that time. The paleoclimate was influenced largely by tectonic events that never existed before or since. At the beginning of the Triassic period, the land masses of the world were still bound together into the vast supercontinent known as Pangaea. Pangaea began to break apart in the mid-Triassic, forming Gondwana (South America, Africa, India, Antarctica, and Australia) in the south and Laurasia (North America and Eurasia) in the north. The movement of the two resulting supercontinents was caused by sea floor spreading at the midocean ridge lying at the bottom of the Tethys Sea, the body of water between Gondwana and Laurasia. While Pangaea was breaking apart, mountains were forming on the west coast of North America by subduction of the ocean plates beneath the continental plates. Throughout the Middle to Late Triassic, mountain forming continued along the coast extending from Alaska to Chile. As mountains were forming on the Americas, North Africa was being split from Europe by the spreading rift. This division of the continents advanced further westward, eventually splitting eastern North America from North Africa. 1. Tectonic and Paleioclimate of Triassic The climate of the Triassic era was influenced by Pangaea, its centralized position stradling the equator, and the geologic activity associated with its breakup. Generally speaking, the continents were of high elevation compared to sea level, and the sea level did not change drastically during the period. Due to the low sea level, flooding of the continents to form shallow seas did not occur. Much of the inland area was isolated from the cooling and moist effects of the ocean. The result was a globally arid and dry climate, though regions near the coast most likely experienced seasonal monsoons. There were no polar ice caps, and the temperature gradient in the north-south direction is assumed to have been more gradual than present day. The sea level rose as the rift grew between 102



North Africa and southern Europe, resulting in the flooding of Central and South Europe; the climates of terrestrial Europe were hot and dry, as in the Permian. Overall, it appears that the climate included both arid dune environments and moist river and lake habitats with gymnosperm forests. Some conclusions can be drawn about more specific regional climates and species based on experimental research. The presence of coal-rich sequences in the high northern and southern latitudes, as well as the presence of large amphibians there, indicates that the paleoclimate was wetter in those areas. Living species of some Mesozoic ferns (including the families Osmundacae and Dipteridacae) now live in wet, shady areas under forest canopies, so it is likely that the paleoclimate their Triassic ancestors inhabitted were also damp and shaded. The Mesozoic era might also have had large, open areas with low-growing vegetation, including savannas or fern prairie with dry, nutrient poor soil populated by herbaceous plants, such as ferns of the families Matoniaceae and Gleicheniaceae. Thus, despite the union of the continental landmasses, the Triassic vegetation was quite provincial, though this decreased as the Triassic wore on. The northern forests at the beginning of the Triassic were dominated by conifers, ginkgos, cycads, and bennettitaleans, while the forests of Gondwana were dominated by Dicroidium and Thinnfeldia. By the end of the Triassic, both hemispheres gave way to conifer and cycad vegetation. The Triassic-Jurassic boundary is similar to the Permo-Triassic boundary in that the global climate was not radically altered, though a major extinction of terrestrial vertebrates occurred. With the end of the Triassic and the beginning of the Jurassic, Pangaea continued to break apart, inevitably affecting the climate, though not as radically as it had during the Triassic. 2. The Triassic Life



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The oceans teemed with the coiled-shelled ammonites, mollusks, and sea urchins that survived the Permian extinction and were quickly diversifying. The first corals appeared, though other reef-building organisms were already present. Giant reptiles such as the dolphin-shaped ichthyosaurs and the long-necked and paddle-finned plesiosaurs preyed on fish and ancient squid. The bottom rung of the food chain was filled with microscopic plants called phytoplankton; two of the major groups still in the oceans today first appeared. Frogs, salamanders, crocodiles, turtles, and snakes slunk and slithered on and off the Triassic coast, lakes, and rivers. Pterosaurs, a group of flying reptiles, took to the air. On firm ground, moss, liverwort, and ferns carpeted forests of conifers, ginkgoes, and palm-like cycads. Spiders, scorpions, millipedes, and centipedes thrived. Grasshoppers appeared. But perhaps the biggest changes came with the evolution of dinosaurs and the first mammals in the late Triassic, starting around 230 million years ago. One of the earliest true mammals was the three-foot-long (one-meterlong) Eozostrodon. The shrewlike creature laid eggs but fed its young mother's milk. Among the first dinosaurs was the two-footed carnivore Coelophysis, which grew up to 9 feet (2.7 meters) tall, weighed up to a hundred pounds (45 kilograms), and probably fed on small reptiles and amphibians. It showed up about 225 million years ago. A few million years later came the 27.5-foot-long (8-meter-long) herbivore called Plateosaurus. The Triassic closed in the same way it began. Something—perhaps a volcanic belch or an asteroid collision—caused another mass extinction. Dinosaurs, however, survived and went on to dominate the Jurassic. B. JURASSIC Great plant-eating dinosaurs roaming the earth, feeding on lush ferns and palm-like cycads and bennettitaleans … smaller but vicious carnivores stalking the 104



great herbivores … oceans full of fish, squid, and coiled ammonites, plus great ichthyosaurs and long-necked plesiosaurs … vertebrates taking to the air, like the pterosaurs and the first birds. This was the Jurassic Period, 199.6 to 145.5 million years ago a 54-million-year chunk of the Mesozoic Era. Named for the Jura Mountains on the border between France and Switzerland, where rocks of this age were first studied, the Jurassic has become a household word with the success of the movie Jurassic Park. Outside of Hollywood, the Jurassic is still important to us today, both because of its wealth of fossils and because of its economic importance — the oilfields of the North Sea, for instance, are Jurassic in age. The largest dinosaurs of the time in fact, the largest land animals of all time were the gigantic sauropods, such as the famous Diplodocus (top right, above), Brachiosaurus and Apatosaurus. Other herbivorous dinosaurs of the Jurassic included the plated stegosaurs. Predatory dinosaurs of the Jurassic included fearsome carnosaurs such as Allosaurus, small, fast coelurosaurs, and ceratosaurs such as Dilophosaurus. The Jurassic also saw the origination of the first birds, including the well-known Archaeopteryx, probably from coelurosaurian ancestors. But there was more to life than dinosaurs! In the seas, the fishlike ichthyosaurs (top left, above) were at their height, sharing the oceans with the plesiosaurs, giant marine crocodiles, and modern-looking sharks and rays. Also prominent in the seas were cephalopods — relatives of the squids, nautilus, and octopi of today. Jurassic cephalopods included the ammonites, with their coiled external shells (upper left), and the belemnites, close relatives of modern squid but with heavy, calcified, bullet-shaped, partially internal shells. Among the plankton in the oceans, the dinoflagellates became numerous and diverse, as did the coccolithophorids (microscopic single-celled algae with an outer covering of calcareous plates). Land plants abounded in the Jurassic, but floras were different from what we see today. Although Jurassic dinosaurs are sometimes drawn with palm trees, 105



there were no palms or any other flowering plants at least as we know them today in the Jurassic. Instead, ferns, ginkgoes, bennettitaleans or "cycadeoids," and true cycads — like the living cycad pictured above, lower left flourished in the Jurassic. Conifers were also present, including close relatives of living redwoods, cypresses, pines, and yews. Creeping about in this foliage, no bigger than rats, were a number of early mammals. C. CRETACEOUS The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants. The breakup of the world-continent Pangea, which began to disperse during the Jurassic, continued. This led to increased regional differences in floras and faunas between the northern and southern continents. The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together. 1. Life No great extinction or burst of diversity separated the Cretaceous from the Jurassic Period that had preceded it. In some ways, things went on as they had. Dinosaurs both great and small moved through forests of ferns, cycads, and conifers. Ammonites, belemnites, other molluscs, and fish were hunted by great "marine reptiles," and pterosaurs and birds flapped and soared in the air above. Yet the Cretaceous saw the first appearance of



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many lifeforms that would go on to play key roles in the coming Cenozoic world. Perhaps the most important of these events, at least for terrestrial life, was the first appearance of the flowering plants, also called the angiosperms or Anthophyta. First appearing in the Lower Cretaceous around 125 million years ago, the flowering plants first radiated in the middle Cretaceous, about 100 million years ago. Early angiosperms did not develop shrub- or tree-like morphologies, but by the close of the Cretaceous, a number of forms had evolved that any modern botanist would recognize. The angiosperms thrived in a variety of environments such as areas with damper climates, habitats favored by cycads and cycadeoids, and riparian zones. High southern latitudes were not invaded by angiosperms until the end of the Cretaceous. Ferns dominated open, dry and/or low-nutrient lands. Typical Jurassic vegetation, including conifers, cycads, and other gymnosperms, continued on into the Lower Cretaceous without significant changes. At the beginning of this period, conifer diversity was fairly low in the higher latitudes of the Northern Hemisphere, but by the middle of the period, species diversification was increasing exponentially. Swamps were dominated by conifers and angiosperm dicots. At about the same time, many modern groups of insects were beginning to diversify, and we find the oldest known ants and butterflies. Aphids, grasshoppers, and gall wasps appear in the Cretaceous, as well as termites and ants in the later part of this period. Another important insect to evolve was the eusocial bee, which was integral to the ecology and evolution of flowering plants. The Cretaceous also saw the first radiation of the diatoms in the oceans (freshwater diatoms did not appear until the Miocene. 2. The Cretaceous-Tertiary extinction



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The most famous of all mass extinctions marks the end of the Cretaceous Period, about 65 million years ago. As everyone knows, this was the great extinction in which the dinosaurs died out, except for the birds, of course. The other lineages of "marine reptiles" — the ichthyosaurs, plesiosaurs, and mosasaurs — also were extinct by the end of the Cretaceous, as were the flying pterosaurs, but some, like the ichthyosaurs, were probably extinct a little before the end of the Cretaceous. Many species of foraminiferans went extinct at the end of the Cretaceous, as did the ammonites. But many groups of organisms, such as flowering plants, gastropods and pelecypods (snails and clams), amphibians, lizards and snakes, crocodilians, and mammals "sailed through" the Cretaceous-Tertiary boundary, with few or no apparent extinctions at all. 3. Tectonics and paleoclimate The Cretaceous is defined as the period between 145.5 and 65.5 million years ago,* the last period of the Mesozoic Era, following the Jurassic and ending with the extinction of the dinosaurs (except birds). By the beginning of the Cretaceous, the supercontinent Pangea was already rifting apart, and by the mid-Cretaceous, it had split into several smaller continents. This created large-scale geographic isolation, causing a divergence in evolution of all land-based life for the two new land masses. The rifting apart also generated extensive new coastlines, and a corresponding increase in the available near-shore habitat. Additionally, seasons began to grow more pronounced as the global climate became cooler. Forests evolved to look similar to present day forests, with oaks, hickories, and magnolias becoming common in North America by the end of the Cretaceous. At the end of the Cretaceous Period, 65 million years ago, an asteroid hit Earth in the Yucatan Peninsula, Mexico, forming what is today called the Chicxulub impact crater. It has been estimated that half of the world's 108



species went extinct at about this time, but no accurate species count exists for all groups of organisms. Some have argued that many of the species to go extinct did so before the impact, perhaps because of environmental changes occuring at this time. Whatever its cause, this extinction event marks the end of the Cretaceous Period and of the Mesozoic Era.



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CHAPTER IX CENOZOIC (TERSIER) A. DEFINITION The Cenozoic Era is the most recent of the three major subdivisions of animal history. The other two are the Mesozoic and Paleozoic Eras. The Cenozoic spans only about 65 million years, from the end of the Cretaceous Period and the extinction of non-avian dinosaurs to the present. The Cenozoic is sometimes called the Age of Mammals, because the largest land animals have been mammals during that time. This is a misnomer for several reasons. First, the history of mammals began long before the Cenozoic began. Second, the diversity of life during the Cenozoic is far wider than mammals. The Cenozoic could have been called the "Age of Flowering Plants" or the "Age of Insects" or the "Age of Teleost Fish" or the "Age of Birds" just as accurately. The Cenozoic (65.5 million years ago to present) is divided into three periods: the Paleogene (65.5 to 23.03 million years ago), Neogene (23.03 to 2.6 million years ago) and the Quaternary (2.6 million years ago to present). Paleogene and Neogene are relatively new terms that now replace the deprecated term, Tertiary. The Paleogene is subdivided into three epochs: the Paleocene (65.5 to 55.8 million years ago), the Eocene (55.8 to 33.9 million years ago), and the Oligocene (33.9 to 23.03 million years ago). The Neogene is subdivided into two epochs: the Miocene (23.03 to 5.332 million years ago) and Pliocene (5.332 to 2.588 million years ago).



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B. DIVISION



Fig. 29. Cenozoic Timeline The Cenozoic is divided into three periods: The Paleogene, Neogene, and Quaternary; and seven epochs: The Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. The Quaternary Period was officially recognized by the International Commission on Stratigraphy in June 2009, and the former Tertiary Period was officially disused in 2004 because of the necessity to divide the Cenozoic into periods more like that of the previous Paleozoic and Mesozoic eras. The common use of epochs during the Cenozoic helps paleontologists better organize and group the many significant events that occurred during this comparatively short interval of time. There is also more detailed knowledge of this era than any other because of the relatively young strata associated with it.



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1. Paleogene The Paleogene spans from the extinction of the dinosaurs, some 66 million years ago, to the dawn of the Neogene twenty three million years ago. It features three epochs: the Paleocene, Eocene and Oligocene. The Paleocene ranged from 65 million to 55 million years ago. The Paleocene is a transitional point between the devastation that is the K-T extinction, to the rich jungles environment that is the Early Eocene. The Early Paleocene saw the recovery of the earth. The continents began to take their modern shape, but all continents (and India) were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama, as the isthmus has not yet formed. This epoch featured a general warming trend, with jungles eventually reaching the poles. The oceans were dominated by sharks as the large reptiles that had once ruled went extinct. Archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over 10 kilograms. Mammals were still quite small. The Eocene Epoch ranged from 55 million years to 33 million years ago. In the Early-Eocene, life was small and lived in cramped jungles, much like the Paleocene. There was nothing over the weight of 10 kilograms. Among them were early primates, whales and horses along with many other early forms of mammals. At the top of the food chains were huge birds, such as Gastornis. It is the only time in recorded history that birds ruled the world (excluding their ancestors, the dinosaurs). The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Mid-Eocene, the circum-Antarctic current between Australia and Antarctica formed which disrupted ocean currents worldwide and as a result caused a global cooling effect, shrinking the jungles. This allowed mammals to grow to mammoth proportions, such as whales which, by that time, were almost fully aquatic. Mammals like 112



Andrewsarchus were at the top of the food-chain and sharks were replaced by whales such as Basilosaurus as rulers of the seas. The Late Eocene saw the rebirth of seasons, which caused the expansion of savanna-like areas, along with the evolution of grass. The Oligocene Epoch spans from 33 million to 23 million years ago. The Oligocene featured the expansion of grass which had led to many new species to evolve, including the first elephants, cats, dogs, marsupials and many other species still prevalent today. Many other species of plants evolved in this period too, such as the evergreen trees. A cooling period was still in effect and seasonal rains were as well. Mammals still continued to grow larger and larger. Paraceratherium, the largest land mammal to ever live evolved during this period, along with many perissodactyls in an event known as the Grande Coupure. 2. Neogene The Neogene spans from 23 million to 3 million years ago, and is the shortest geological period in the Phanerozoic Eon. It features 2 epochs: the Miocene, and the Pliocene. The Miocene spans from 23 to 5 million years ago and is a period in which grass spread further across, effectively dominating a large portion of the world, diminishing forests in the process. Kelp forests evolved, leading to new species such as sea otters to evolve. During this time, perissodactyls thrived, and evolved into many different varieties. Alongside them were the apes, which evolved into a staggering 30 species. Overall, arid and mountainous land dominated most of the world, as did grazers. The Tethys Sea finally closed with the creation of the Arabian Peninsula and in its wake left the Black, Red, Mediterranean and Caspian Seas. This only increased aridity. Many new plants evolved, and 95% of modern seed plants evolved in the mid-Miocene. The Pliocene lasted from 5 to 2 million years ago. The Pliocene featured dramatic climactic changes, which ultimately lead to modern



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species and plants. The Mediterranean Sea dried up for several million years. Along with these major geological events, Australopithecus evolved in Africa, beginning the human branch. The isthmus of Panama formed, and animals migrated between North and South America, wreaking havoc on the local ecology. Climatic changes brought savannas that are still continuing to spread across the world, Indian monsoons, deserts in East Asia, and the beginnings of the Sahara desert. The earth's continents and seas moved into their present shapes. The world map has not changed much since. 3. Quaternary The Quaternary spans from 3 million to present day, and features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene. The Pleistocene lasted from 3 million to 12,000 years ago. This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene. There were at least four separate glaciation periods marked by the advance of ice caps as far south as 40 degrees N latitude in mountainous areas. Meanwhile, Africa experienced a trend of desiccation which resulted in the creation of the Sahara, Namib, and Kalahari deserts. Many animals evolved including mammoths, giant ground sloths, dire wolves, saber-toothed cats, and most famously Homo sapiens. 100,000 years ago marked the end of one of the worst droughts of Africa, and led to the expansion of primitive man. As the Pleistocene drew to a close, a major extinction caused wiped out much of the world's megafauna, including some of the hominid species, such as Neanderthals. All the continents were affected, but Africa to a lesser extent. The continent retains many large animals, such as hippos. The Holocene began 12,000 years ago and lasts until to present day. Also known as "the Age of Man", the Holocene is marked by the rise of man on his path to sentience. All recorded history and "the history of the 114



world" lies within the boundaries of the Holocene epoch. Human activity is blamed for a mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution. This is sometimes referred to as the "Sixth Extinction". 322 species have become extinct due to human activity since the Industrial Revolution. C. TEKTONIC AND PALEOCLIMATE Geologically, the Cenozoic is the era when the continents moved into their current positions. Australia-New Guinea, having split from Pangea during the early Cretaceous, drifted north and, eventually, collided with South-east Asia; Antarctica moved into its current position over the South Pole; the Atlantic Ocean widened and, later in the era, South America became attached to North America with the isthmus of Panama. India collided with Asia 55 to 45 million years ago creating the Himalayas; Arabia collided with Eurasia, closing the Tethys ocean and creating the Zagros Mountains, around 35 million years ago. The Paleocene–Eocene Thermal Maximum of 55.8 million years ago was a significant global warming event; however, since the Azolla event of 49 million years ago, the Cenozoic Era has been a period of long-term cooling. After the tectonic creation of Drake Passage, when South America fully detached from Antarctica during the Oligocene, the climate cooled significantly due to the advent of the Antarctic Circumpolar Current which brought cool deep Antarctic water to the surface. The cooling trend continued in the Miocene, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents, eventually leading to the glaciations of the Quaternary ice age, the current interglacial of which is the Holocene Epoch.



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D. BIOTA EVOLUTION The survivors of the Cretaceous/Tertiary catastrophe included some small, squirrel-like animals that were to give rise to the dominant life forms of the next era the fur-bearing, warm-blooded mammals that eventually gave rise to the human species. The period between the extinction of the dinosaurs and the present day is called the Age of Mammals or Cenozoic. Mammals appeared on the earth long before the extinction of the dinosaurs; in fact, dinosaurs and mammals originated within 10 million years of each other, in the late Triassic about 200 million years ago. By late Cretaceous small primitive marsupials (mammals that brood their young in a pouch, like opossums), and insectivores, similar to shrews and hedgehogs, were quite abundant and widespread. But only after the dinosaurs were gone did the mammals begin their great diversification and become the dominant land animals. Then, within 10 million years, there were mammals of all kinds living in many different habitats on land, in the sea and in the air. There were herbivores, carnivores, whales, bats. During the Cenozoic there was also tremendous radiation in other groups including birds, reptiles, amphibians and fish, leading gradually up to the peak of biological diversity that occurred in the recent past. The geography of the world changed dramatically during the time when animals and plants were evolving. The major continental land masses were initially fused together into one giant continent named Pangaea during the Paleozoic era. In the Mesozoic, Pangaea gradually broke up into the present-day continents, which have been moving apart from each other, by continental drift, ever since. This idea of continental drift was first based on the remarkably close fit between the coastlines of major continents, most notably the west coast of Africa with the east coast of South America. It is now supported by measurements, which show that the continents on either side of the Atlantic Ocean are still moving apart from one another, at the rate of several centimeters per year. Continental drift was actually a little more complicated, with the North American plate drifting around in the Pacific 116



Ocean for quite a long time. A large chunk of the North American plate was recently found in Argentina, left there after the two continents bumped into each other then moved apart. Learn more about This Dynamic Earth. The separation of the great land mass into different continents allowed biological evolution to take quite different paths in different parts of the world. And the formation of oceanic islands, often by volcanic activity, produced many more isolated areas where evolution could experiment with different forms. Breakdown of this isolation, either by geological changes or by transport of organisms between the isolated areas, has often led to extinction of the endemic forms, and so loss of diversity. During the Cenozoic era (the last 66 million years), there was a gradual lowering of temperatures as well as the gradual establishment of different climatic zones of the earth -the tropics, the temperate zones and the cool climates of the higher latitudes. The culmination of the cooling trend was the Pleistocene epoch, or Great Ice Age, of the last 1.8 million years. During this time vast expanses of North America and Eurasia were periodically covered with enormous continental glaciers. These glaciers advanced during the four ice ages (glacial periods) and retreated during the three interglacials. We are probably now living in the fourth interglacial stage. During the glacial periods the sea level became much lower because so much water was converted to ice. Consequently land bridges, especially the Bering land bridge across the Bering Sea joining Asia with North America, became available for animal migrations. During the Cenozoic the mammals reached their peak of evolution, producing a tremendous variety of species, many of them very large. The segment of the fauna containing these large creatures (those weighing more than about 100 pounds) is called the Megafauna. Most of these animals are extinct. E. HOMINOID DEVELOPMENT IN CENOZOIC The first hominids (i.e. creatures more closely related to humans than to apes) lived from 4 to 3 million years ago. These (called Australopithecus) lived in Africa. 117



They had a protruding jaw, prominent eyebrow ridges and a small braincase. They walked upright. 1.8 million years ago, Homo erectus appeared in Africa, with a brain as big as the smallest modern human brain. H. erectus differed from modern humans by the prominent brow ridges and receding chin. They made sophisticated stone hand-axes with sharp edges, possibly made spear points, and probably used fire. They spread over Africa and Asia and survived until about 400,000 years ago. F. QUARTER HUMAN DEVELOPMENT At the start of the Quaternary, the continents were just about where they are today, slowing inching here and there as the forces of plate tectonics push and tug them about. But throughout the period, the planet has wobbled on its path around the sun. The slight shifts cause ice ages to come and go. By 800,000 years ago, a cyclical pattern had emerged: Ice ages last about 100,000 years followed by warmer interglacials of 10,000 to 15,000 years each. The last ice age ended about 10,000 years ago. Sea levels rose rapidly, and the continents achieved their present-day outline. When the temperatures drop, ice sheets spread from the Poles and cover much of North America and Europe, parts of Asia and South America, and all of Antarctica. With so much water locked up as ice, sea levels fall. Land bridges form between the continents like the currently submerged connector across the Bering Strait between Asia and North America. The land bridges allow animals and humans to migrate from one landmass to another. During warm spells, the ice retreats and exposes reshaped mountains striped with new rivers draining to giant basins like today's Great Lakes. Plants and animals that sought warmth and comfort toward the Equator return to the higher latitudes. In fact, each shift alters global winds and ocean currents that in turn alter patterns of precipitation and aridity around the world.



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Since the outset of the Quaternary, whales and sharks have ruled the seas, topping a food chain with otters, seals, dugongs, fish, squid, crustaceans, urchins, and microscopic plankton filling in the descending rungs. On land, the chilliest stretches of the Quaternary saw mammals like mammoths, rhinos, bison, and oxen grow massive and don shaggy coats of hair. They fed on small shrubs and grasses that grew at the ever moving edges of the ice sheets. About 10,000 years ago, the climate began to warm, and most of these so-called megafauna went extinct. Only a handful of smaller, though still impressively large, representatives remain, such as Africa's elephants, rhinoceroses, and hippopotamuses. Scientists are uncertain whether the warming climate is to blame for the extinction at the end of the last ice age. At the time, modern humans were rapidly spreading around the globe and some studies link the disappearance of the big mammals with the arrival of humans and their hunting ways. In fact, the Quaternary is often considered the "Age of Humans." Homo erectus appeared in Africa at the start of the period, and as time marched on the hominid line evolved bigger brains and higher intelligence. The first modern humans evolved in Africa about 190,000 years ago and dispersed to Europe and Asia and then on to Australia and the Americas. Along the way the species has altered the composition of life in the seas, on land, and in the air and now, scientists believe, we're causing the planet to warm. Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. Humans and the great apes (large apes) of Africa chimpanzees (including bonobos, or so-called “pygmy chimpanzees”) and gorillas share a common ancestor that lived between 8 and 6 million years ago. Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa.



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Most scientists currently recognize some 15 to 20 different species of early humans. Scientists do not all agree, however, about how these species are related or which ones simply died out. Many early human species -- certainly the majority of them – left no living descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species. Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. The first fossils that are classified in the modern species Homo sapiens date from about 200,000 years ago (Nat. Geog. , Jan. 1996) and are called neanderthals (a subspecies of Homo sapiens). The neanderthals still looked primitive, with prominent brow ridges, low foreheads, and receding chins, but their brains were, on average, slightly larger than ours. They hunted woolly rhino and cave-bear and disappeared about 30,000 years ago. About 30,000 years ago, fully modern humans called Cro-Magnon evolved from the neanderthal-like forms of the Near East and spread into Asia and Europe, rapidly replacing the more primitive neanderthals. They had domed heads, smooth brows, and prominent chins. They made precision tools, including definite spearheads, and they produced spectacular works of wildlife art on the walls of caves, which provide some glimpses of how the big game was hunted - with spears and rocks and probably also traps and fire. One painting shows an eviscerated bison about to gore a human.



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