Geological Time Scale Written Report - Technological University of the Philippines - Manila

Republic of the Philippines Technological University of the Philippines – Manila 1000 Ayala Boulevard cor. San Marcelino St., Ermita, Manila College of Engineering Department of Civil Engineering PCS2-M Professional Course - Specialized 2 (Earthquake Engineering) Written Report GEOLOGICAL TIME SCALE Submitted by: Baquero, Angela T. Mogan, Alyssa Jhoi S. Rasco, Honney Lyn R. Ripalda, Jolex M. Ybañez, Charles Miguel A. BSCE 4A Submitted to: Engr. Edmundo C. Dela Cruz Date Submitted: September 24, 2024 I. INTRODUCTION TO GEOLOGICAL TIME SCALE DEFINITION The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet. The geologic time scale is the “calendar” for events in Earth history. It subdivides all time into named units of abstract time called—in descending order of duration—eons, eras, periods, epochs, and ages. The enumeration of those geologic time units is based on stratigraphy, which is the correlation and classification of rock strata. These divisions are called geochronologic units (geo: rock, chronology: time). The fossil forms that occur in the rocks, however, provide the chief means of establishing a geologic time scale, with the timing of the emergence and disappearance of widespread species from the fossil record being used to delineate the beginnings and endings of ages, epochs, periods, and other intervals. One of the most widely used standard charts showing the relationships between the various intervals of geologic time is the International Chronostratigraphic Chart, which is maintained by the International Commission on 1 Stratigraphy (ICS). Figure 1. Geologic Time Scale Illustration from ICS PRINCIPLES BEHIND GEOLOGIC TIME SCALE Nicholas Steno, a Danish physician (1638-1687), described how the position of a rock layer could be used to show the relative age of the layer. He devised the three main principles that underlie the interpretation of geologic time: ○ The principle of superposition: The layer on the bottom was deposited first and so is the oldest. ○ The principle of horizontality: All rock layers were originally deposited horizontally. ○ The principle of original lateral continuity: Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer. Figure 2. Nicholas Steno Decades later, other European scientists rediscovered 'Steno’s Laws' and began applying them. Abraham Gottlob Werner became famous for his proposal that all rocks came from the ocean environment. He and his followers were called "Neptunists." An opposing view (by Voisins) argued that all rocks of the Earth came from volcanic environments. These scientists were called "Plutonists." 2 Figure 3. Abraham Gottlob Werner James Hutton, a Scottish physician and geologist (1726-1797), thought the surface of the Earth was an ever-changing environment and "the past history of our globe must be explained by what can be seen to be happening now." This theory was called "uniformitarianism", later catch-phrased as "the present is the key to the past." Figure 4. James Hutton William Smith was a surveyor who was in charge of mapping a large part of England. He was the first to understand that certain rock units could be identified by the particular assemblages of fossils they contained. Using this information, he was able to correlate strata with the same fossils for many miles, giving rise to the principle of biologic succession: ○ The principle of biologic succession: Each age in the Earth’s history is unique such that fossil remains will be unique. This permits vertical and horizontal correlation of the rock layers based on fossil species. 3 Figure 5. William Smith During the early 1800’s, English geologist Charles Lyell published a book called "Principles of Geology," which became a very important volume in Great Britain. It included all of Hutton’s ideas and presented his own contemporary ideas such as: ○ The principle of cross-cutting relationships: A rock feature that cuts across another feature must be younger than the rock that it cuts. ○ Inclusion principle: Small fragments of one type of rock embedded in a second type of rock must have formed first and were included when the second rock was forming. Figure 6. Charles Lyell 4 Charles Darwin (1809-1882) was an unpaid naturalist who signed up for a 5-year expedition around the world aboard the H.M.S. Beagle. On this trip, he realized two major points: 1. In spite of all species reproducing, no one species overwhelmed the Earth, concluding that not all individuals produced in a generation survive. 2. Individuals of the same kind differ from one another, and he concluded that those with the most favorable variations would have the best chance of surviving to create the next generation. Figure 7. Charles Darwin The theory of natural selection was credited to Darwin (along with Alfred Russel Wallace), and he went on to write the famous "Origin of Species." Darwin’s two goals in that work were: 1. To convince the world that evolution had occurred and organisms had changed over geologic time. 2. The mechanism for this evolution was natural selection. 5 Figure 8. Alfred Russel Wallace METHODS USED TO DETERMINE THE FOSSILS AGE 1. Relative Age Dating This method compares the age of one object or layer to another. It uses stratigraphic principles to determine the sequence of rock layers, establishing a relative timeline for their formation. For example, older layers are found below younger layers. 2. Relative Age Dating with Index Fossils Index fossils are fossils of organisms that lived for a short time but were widespread. These fossils allow geologists to correlate rock layers across large distances. Trilobites are a common index fossil, which helps scientists match layers and estimate their age. 3. Absolute Age Dating 6 Unlike relative dating, absolute age dating assigns a specific number of years to a rock or fossil. This is done through analyzing the isotopes in the rock. By understanding the rate at which radioactive elements decay, scientists can measure the age of rocks in years. Isotopes decay at a constant rate, and the time it takes for half of a given amount of radioactive material to decay is called the half-life. By measuring the remaining amount of parent and daughter isotopes, scientists can calculate how long the decay process has been occurring and, thus, the age of the rock. 4. Radiocarbon Dating This method is used to date materials that were once alive. Carbon-14 decays over time, and by measuring the remaining C-14 in organic material, scientists can determine its age, up to about 70,000 years. This technique is used for dating fossils, wood, and other organic matter. 5. Uranium-Lead Decay Series (U-Pb Series) Uranium isotopes, specifically U-235 and U-238, are commonly used in dating igneous rocks. Over time, uranium decays into lead, and by measuring the ratio of uranium to lead, scientists can determine the age of the rock. This method is especially useful for dating rocks that are millions or even billions of years old. DIVISIONS OF GEOLOGIC TIME SCALE Earth’s age is approximately 4.5 billion years so that’s why we use billions, millions, and thousands of years as time markers. Typically, we use abbreviations like ‘Ga’ (giga-annum), ‘Ma’ (mega-annum), and ‘Ka’ (kilo-annum). ‘Ga’ or ‘Gya’ (billion) is 1,000,000,000 years ago ‘Ma’ or ‘Mya’ (million) is 1,000,000 years ago ‘Ka’ or ‘Kya’ (thousand) 1,000 years ago Eons Eons are the longest division of geologic time. Generally, we measure eons as billions of years ago (Ga) and millions of years ago (Ma). Geologists divide the lifespan of Earth into a total 7 of 4 eons. From origin to now, Earth’s 4 eons are the Hadean, Archean, Proterozoic and Phanerozoic Eon. The Hadean, Archean and Proterozoic eons are sometimes grouped as the Precambrian Eon. Eras Eras are divisions of geologic time shorter than eons but longer than periods. In terms of geochronological units, there are 10 defined eras that generally span several hundred million years. For example, the Paleozoic, Mesozoic, and Cenozoic eras are within the Phanerozoic Eon. Periods There are 22 defined periods. Periods are divisions of geologic time longer than epochs but shorter than an era. Each period spans a length of tens to one hundred million years. Next, there are 34 defined epochs which generally last for tens of millions of years. The geologic time scale conceptually consists of periods that we break down into smaller epochs. Epochs Epochs are then divided into ages, which are the shortest division of geologic time. In terms of the number of geochronological units, there are 99 defined which can stretch over millions of years. Epochs contain minor differences between each unit. Some geologists divide ages even further. If you do so, chrons are the smallest working geochronological unit. However, these are less common. II. Major Divisions of the Geological Time Scale 8 The broadest category of geological time is the eon. There are four eons that define Earth's history; the Hadean, Archean, Proterozoic, and Phanerozoic are the oldest to youngest. Since the Cambrian period marks the start of the Phanerozoic eon, all rocks older than the Cambrian are Precambrian in age. Together, the Hadean, Archean, and Proterozoic are frequently referred to as the "Precambrian." Figure 9. Geological Time Scale - Eons 1. Precambrian Eon The longest and earliest period in Earth's history, the Precambrian Eon, lasted from 4.6 billion years to 541 million years. It covers almost 88% of the historical era on Earth. The Precambrian Eon is divided into three main divisions: the Hadean, Archean, and Proterozoic Eons. a. Hadean Eon The Hadean Eon is an informal division of Precambrian time spanning from approximately 4.6 billion to 4.0 billion years in the past. The stabilization of Earth's core and crust, the formation of its atmosphere and oceans, and the planet's original formation from the accumulation of dust and gasses and repeated 9 collisions with larger planetesimals are the characteristics of the Hadean Eon. Massive amounts of heat were produced during a portion of the eon by impacts from alien bodies, which probably stopped much of the granite from hardening at the surface. As a result, the interval's name alludes to Hades, which is the Greek term for hell that comes from the Hebrew. In the early Hadean Eon, the surface of the Earth was extremely unstable. Melting rock ascended to the surface of the mantle due to convection currents, while cooling rock descended into magmatic seas. Lighter elements, like silicon, rose and were absorbed into the expanding crust, while heavier elements, like iron, dropped to become the core. While the exact formation date of the planet's outer crust remains unknown, some scientists assert that the discovery of a few zircon grains, which date to approximately 4.4 billion years ago, confirms the existence of stable continents, liquid water, and surface temperatures that were likely below 100 °C (212 °F). A number of ideas on the Moon's origin have been proposed. It is also believed that the Moon formed during the Hadean Eon. The dominant explanation states that material that eventually came to form the Moon was ejected by an impact between Earth and a celestial body the size of Mars. 10 Figure 10. Hadean Eon b. Archean Eon The earliest of the two official divisions of Precambrian time, known as the Archean Eon, lasted from roughly 4.6 billion to 541 million years ago and is when life first appeared on Earth. The construction of Earth's crust marked the beginning of the Archean Eon, which lasted for approximately 4 billion years. The Proterozoic Eon, the second official division of Precambrian time, began 2.5 billion years ago. The Hadean Eon, an imprecise division of geologic time that encompasses Earth's early genesis and dates from around 4.6 billion to 4 billion years ago, came before the Archean Eon. The early Archean (Eoarchean Era) is when records of Earth's primordial waters and atmosphere first appear. Although ancient fragments of graphite, which may have been produced by microbes, suggest that life may have emerged before 3.95 billion years ago, fossil evidence of the earliest primitive life-forms— prokaryotic microbes from the domain called Archaea and bacteria—appear in rocks that are roughly 3.5–3.7 billion years old. Gold and silver are among the many valuable mineral resources found in archean greenstone-granite belts. The isotopic age of the earliest rocks is the only factor that can determine when the Archean Eon began. Earth was in the astronomical (Hadean) stage of planetary accretion, which started around 4.6 billion years ago, before the Archean Eon; no rocks have survived from this stage. Minerals, not rocks, were the first materials to form on Earth. Relict detrital zircon grains with isotopic ages ranging from 4.2 to 4.4 billion years have been found in certain sedimentary conglomerates in Western Australia, which are dated to 3.3 billion years ago. Rivers had to have carried these grains from an unidentified source place; it could have been destroyed by meteorite strikes, which were common on Earth and the Moon before 4 billion years ago. 11 It is believed that the oxygen in the atmosphere today must have gradually built up throughout geological time, beginning with an anoxic atmosphere during the Archean period. Volcanoes release a lot of carbon dioxide (CO2) and water vapor (H2O), but very little free oxygen (O2). Only a minor amount of free oxygen would have been created by the inorganic breakdown (photodissociation) of carbon dioxide and water vapor originating from volcanic eruptions in the atmosphere. Anaerobic cyanobacteria, or blue-green algae, produced oxygen as a byproduct of their organic photosynthesis of carbon dioxide (CO2) and water (H2O), which provided the majority of the free oxygen in the Archean atmosphere. These creatures were prokaryotes, a class of unicellular creatures that emerged at the close of the Archean Eon and had simple internal organization. The activities that were taking place in Earth's oceans towards the end of the Archean helped set the stage for the increase in atmospheric oxygen, even though oxygen did not accumulate in the atmosphere in any significant amount until early Proterozoic time. It is most likely that water from the emissions of several volcanoes condensed to form the Archean oceans. Then, as now, iron was released into the oceans during the formation of thick oceanic plateaus and from undersea volcanoes located in oceanic ridges. Figure 11. Archean Eon 12 c. Proterozoic Eon The younger of the two divisions of Precambrian time, the Archean Eon, is known as the Proterozoic Eon. The Paleoproterozoic (2.5 billion to 1.6 billion years ago), Mesoproterozoic (1.6 billion to 1 billion years ago), and Neoproterozoic (1 billion to 541 million years ago) eras are commonly used to categorize the Proterozoic Eon, which spanned 2.5 billion to 541 million years ago. All of the continents have been found to contain proterozoic rocks, which are frequently significant sources of metallic ores, including nickel, uranium, copper, gold, and iron. The Proterozoic brought about major changes to the climate and oceans. Proterozoic rocks have numerous unmistakable remnants of ancient life, including the earliest organisms that required oxygen, the Ediacara fauna, and the fossilized remains of bacteria and blue-green algae. Figure 12. Proterozoic Eon 13 2. Phanerozoic Eon The period of geologic time between the end of the Proterozoic Eon, which started around 2.5 billion years ago, and the present, or the Phanerozoic Eon. The eon of visible life, known as the Phanerozoic, is split into three main periods of time, the Paleozoic (541 million to 252 million years ago), Mesozoic (252 million to 66 million years ago), and Cenozoic (66 million years ago to the present), primarily based on distinctive groups of life-forms. While it is evident that life began at some point, most likely very early in the Archean Eon (4 billion to 2.5 billion years ago), it was not until the Phanerozoic that forms began to rapidly expand and evolve to fill the many ecological niches that became available. It seems that the development of plants capable of photosynthetic respiration— which releases free oxygen into the atmosphere—was the key to that huge Phanerozoic expansion. Before then, there was very little free oxygen in the Earth's atmosphere, which prevented animals from developing because they depend on breathing for energy exchanges. Throughout the Phanerozoic, activities including continental drift, mountain formation, and continental glaciation helped Earth progressively take on its current structure and physical characteristics. Therefore, even though the Phanerozoic Eon only makes up roughly the final eighth of the period since the formation of the Earth's crust, its significance vastly outweighs its brief lifetime. 14 Figure 13. Phanerozoic Eon PALEOZOIC ERA During the Paleozoic Era, which took up over half of the Phanerozoic, which lasted almost 300 million years, plants and reptiles began moving from the sea to the land. The era has been divided into six periods: Permian, Carboniferous, Devonian, Silurian, Ordovician, and Cambrian. The Paleozoic is bracketed by two of the most important events in the history of animal life. At its beginning, multi celled animals underwent a dramatic "explosion" in diversity, and almost all living animal phyla appeared within a few millions of years. At the other end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species. CAMBRIAN PERIOD (541 million years ago to 485 million years ago) Figure 14. Cambrian Period This is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion," because of the relatively short time over which this diversity of forms appears. 15 LIFE Almost every metazoan phylum with hard parts, and many that lack hard parts, made its first appearance in the Cambrian. A few mineralized animal fossils, including sponge spicules and probable worm tubes, are known from the Ediacaran Period immediately preceding the Cambrian. Cambrian was nonetheless a time of great evolutionary innovation, with many major groups of organisms appearing within a span of only forty million years. Trace fossils made by animals also show increased diversity in Cambrian rocks, showing that the animals of the Cambrian were developing new ecological niches and strategies — such as active hunting, burrowing deeply into sediment, and making complex branching burrows. Finally, the Cambrian saw the appearance and/or diversification of mineralized algae of various types, such as the coralline red algae and the dasyclad green algae. STRATIGRAPHY Animals showed dramatic diversification during this period of Earth's history. Animals showed dramatic diversification during this period. When the fossil record is scrutinized closely, it turns out that the fastest growth in the number of major new animal groups took place during early Cambrian, a period of about 13 million years. In that time, the first undoubted fossil annelids, arthropods, brachiopods, echinoderms, molluscs, onychophorans, poriferans, and priapulids show up in rocks all over the world. Stratigraphic boundaries are generally determined by the occurrences of fossils. For instance, the trace fossil Treptichnus pedum marks the base of the Cambrian. TECTONICS AND PALEOCLIMATE World climates were mild; there was no glaciation. Landmasses were scattered as a result of the fragmentation of the supercontinent Rodinia that had existed in the late Proterozoic. Most of North America lay in warm southern tropical and temperate latitudes, which supported the growth of extensive shallow-water archaeocyathid reefs all through the early Cambrian. Siberia, which also supported abundant reefs, was a separate continent due east of North America. Baltica — what is now Scandinavia, eastern Europe, and European Russia — lay to the south. Most of the rest of the continents were 16 joined together in the supercontinent Gondwana, depicted on the right side of the map. What is now China and east Asia was fragmented at the time, with the fragments visible north and west of Australia. Western Europe was also in pieces, with most of them lying northwest of what is now the north African coastline. The present-day southeastern United States are visible wedged between South America and Africa. Tectonism affected regions of Gondwana, primarily in what are now Australia, Antarctica, and Argentina. The continental plate movement and collisions during this period generated pressure and heat, resulting in the folding, faulting, and crumpling of rock and the formation of large mountain ranges. ORDOVICIAN PERIOD (485 million years to 443 million years ago) Figure 15. Ordovician Period The Ordovician Period lasted almost 45 million years. 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. 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 characterized the end of the Ordovician in which 60% of all marine invertebrate genera and 25% of all families went extinct. 17 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. 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. 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 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. 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 supercontinent 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 18 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, 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 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. SILURIAN PERIOD (443 million years to 419 million years ago) Figure 16. Silurian Period 19 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. 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. 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. 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. 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. 20 The Llandovery (443.7-428.2 million years ago) preserves its fossils in shale, sandstone, and gray mudstone sediment. Its base (beginning) is 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. 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, while Australia and Scandinavia resided in the tropics; South America and Africa were over the South Pole. 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. 21 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. DEVONIAN PERIOD (419 million years to 359 million years ago) Figure 17. Devonian Period The vegetation of the early Devonian consisted primarily of small plants, the tallest being only a meter tall. By the end of the Devonian, ferns, horsetails and seed plants had also appeared, producing the first trees and the first forests. LIFE 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. 22 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 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. 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. 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. 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. 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 world-continent Pangea in the Permian. 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 23 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. CARBONIFEROUS PERIOD (359 million years to 299 million years ago) Figure 18. Carboniferous Period 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. LIFE 24 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. Trilobites were increasingly scarce while foraminifera 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 bryozoans, 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. 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. 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 25 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. 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. PERMIAN PERIOD (299 million years to 252 million years ago) Figure 19. Permian Period Permian marine animal fossils include mollusks, brachiopods, bryozoans, crinoids, coral, sharks’ teeth, and one-cell fusulinids. Terrestrial leaf and insect fossils have been found. Mass extinction occurred at the end of this period. LIFE 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. 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 26 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. 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). 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 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. MESOZOIC ERA Mesozoic means "middle animals," and is the time during which the world's fauna changed drastically from that which had been seen in the Paleozoic. Dinosaurs, which are perhaps the most popular organisms of the Mesozoic, evolved in the Triassic, but were not very diverse until the Jurassic. Except for birds, dinosaurs became extinct at the end of the Cretaceous. Some of the last dinosaurs to have lived are found in the late Cretaceous deposits of Montana in the United States. The Mesozoic was also a time of great change in the terrestrial vegetation. The early Mesozoic was dominated by ferns, cycads, ginkgophytes, bennettitaleans, and other unusual plants. Modern gymnosperms, such as conifers, first appeared in their current recognizable forms in the early Triassic. By the middle of the Cretaceous, the earliest angiosperms had appeared and began to diversify, largely taking over from the other plant groups. 27 TRIASSIC PERIOD (251 million years to 199.6 million years ago) Figure 20. Triassic Period LIFE 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. At the beginning of the Triassic Period, the land masses of the world were still bound together into the vast supercontinent known as Pangea. Pangea began to break apart in the Middle 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 mid ocean ridge lying at the bottom of the Tethys Sea, the body of water between Gondwana and Laurasia. While Pangea was breaking apart, mountains were forming on the west coast of North America by subduction of the ocean plates beneath 28 the continental plates. Throughout the Middle to Upper Triassic, mountain-forming continued along the coast extending from Alaska to Chile. As mountains were forming in 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. The climate of the Triassic Period was influenced by Pangea, its centralized position straddling the equator, and the geologic activity associated with its breakup. JURASSIC PERIOD (199.6 million years to 145 million years ago) Figure 21. Jurassic Period 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. LIFE It is quite true that the dinosaurs dominated the land fauna. The largest dinosaurs of the time — in fact, the largest land animals of all time — were the gigantic sauropods, such as the famous Diplodocus, 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 29 ceratosaurs such as Dilophosaurus. The Jurassic also saw the origination of the first birds, including the well-known Archaeopteryx, probably from coelurosaurian ancestors. In the seas, the fishlike ichthyosaurs 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, 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). CRETACEOUS PERIOD (145 million years to 65 million years ago) Figure 22. Cretaceous Period 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. 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. 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 30 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. 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-Tertiary extinction 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. TECTONICS AND PALEOCLIMATE 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 31 look similar to present day forests, with oaks, hickories, and magnolias becoming common in North America by the end of the Cretaceous. CENOZOIC ERA The Cenozoic Era, also known as the “Age of Mammals”, is a geological era that began about 66 million years ago and continues to the present. The term Cenozoic, originally spelled “Kainozoic”, was introduced by British geologist John Phillips in an 1840 entry in the Penny Cyclopedia. The name is derived from the Greek phrase meaning “recent life” which reflects the sequential development and diversification of life on Earth from the Paleozoic (ancient life) through the Mesozoic (middle life). Today, the Cenozoic is internationally accepted as the youngest of the three subdivisions of the fossiliferous part of Earth history. The Cenozoic Era is divided into three periods: the Paleogene, Neogene, and the Quaternary. The era has been originally divided into the Tertiary and Quaternary periods; however, Paleogene and Neogene are relatively new terms that now replace the deprecated term, Tertiary. GEOLOGIC PERIOD OF CENOZOIC ERA a. PALEOGENE PERIOD The Paleogene Period, spanning from 66 million to 23 million years ago, marks the first chapter of the Cenozoic Era. It is subdivided into three epochs: the Paleocene, the 32 Eocene, and the Oligocene. This period witnessed the recovery of life following the mass extinction event that ended the Mesozoic Era, wiping out the non-avian dinosaurs. Figure 23. Paleogene Period GEOLOGIC EPOCH OF PALEOGENE PERIOD i. PALEOCENE EPOCH (66 MYA to 56 MYA) Earth’s Appearance: Sea level fell to expose the dry land on much of inland North America, Europe, Africa, and Australia.By the end of the Paleocene, North America’s last large island sea was gone. South America, Antarctica, Australia, India, and Africa were all separate continents. Climate: The climate during the Paleocene was much warmer and more uniform than today. At the end of the Paleocene there was a sudden global warming. The exact cause for this temperature increase is unknown but may be related to the release of carbon dioxide (CO2) and methane (CH4) into the oceans and atmosphere. Moreover, atmospheric and ocean circulation patterns changed, and there were significant extinctions in some deep-sea organisms and a major turnover in land mammal species. Animals and Plants After the massive extinction at the end of the Cretaceous, evolution once again proceeded rapidly. With their dinosaur competitors gone, many new 33 mammals evolved. The first rodents, armadillos, primitive primates, and ancestors to modern mammalian carnivores appeared. However, none of these Paleocene forms were any bigger than a small bear. Many of these early mammals were unsuccessful competitors, and few exist today. Although the dinosaurs were gone, reptiles, such as snakes, lizards, turtles, and crocodiles persisted. On the other hand, new plants quickly evolved, and the first pines, cacti, and palm trees appeared. Flowering plants continued to diversify rapidly. ii. EOCENE EPOCH (56 MYA to 34 MYA) Earth’s Appearance: At the beginning of the Eocene, India, which had been moving slowly northward, collided with Asia, and this force started to push up the Himalayan Mountains. Australia rifted away from Antarctica and began to move northward. By the end of the Eocene, the gap between these two continents was large enough that the Circum-Antarctic Current first started flowing. This changed ocean currents around the world and resulted in a global cooling event at the end of the Eocene. Sea level was high during much of the Eocene, which submerged large portions of most continents. Climate: During the Eocene, temperatures were warmer than during any other time in the Cenozoic. There was a lot of rainfall but no seasons, no glaciers, and similar temperatures throughout most of the globe. Palm trees and alligators were able to live within the Arctic Circle. By the end of the Eocene, temperatures had dropped drastically, and seasonality had returned. This had profound effects on the plants and animals. Animals and Plants: 34 The increase in diversity of mammals that began in the Paleocene continued in the Eocene. The first whales, bats, primitive elephants, and hoofed animals appeared. The first giant mammals roamed the Earth. The first horse-like animals lived in the Eocene, but they were the size of dogs and had toes instead of hooves. Eocene primates more closely resembled modern forms. Birds also continued to diversify with the appearance of penguins, pelicans, ducks, and gulls. The highly successful flowering plants continued to diversify until they filled most environments on the land. iii. OLIGOCENE EPOCH (34 MYA to 23 MYA) Earth’s Appearance: More of North America was dry land than in the preceding Eocene Epoch. The Gulf Coast remained flooded, but the Atlantic Coast north of South Carolina was dry land during most of this time. India pushed farther into Asia, South America separated from Antarctica, and Australia continued to move away from Antarctica. There was a significant increase in volcanic activity in Europe and in North America. Yellowstone National Park is a remnant of this activity. Climate: The climate, which had been warm and moist in the Eocene, became cool, dry, and seasonal. For the first time in the Cenozoic, Antarctica was covered extensively with glaciers, which lowered sea level. Farther north, temperate forests replaced subtropical forests. Near the end of the Oligocene, savannas (grasslands with scattered trees) appeared. Animals and Plants: As temperatures lowered, seasonality increased, grasslands appeared, and the body size of mammals increased. A huge, hornless rhinoceros from Asia was the largest land mammal ever to live. As forests diminished, some animal species 35 adapted and became grazers. Many species could not survive the change in climate and perished. Many other new forms evolved that could cope with the savanna's limited hiding places. Early forms of monkeys, dogs, cats, rhinoceroses, pigs, and camels were present. Horses increased in size, with longer legs and fewer toes for faster running. The cooler, drier, more seasonal climate of the Oligocene was ideal for the evolution of numerous species of grasses. b. NEOGENE PERIOD The Neogene Period, spanning from 23 million to 2.6 million years ago, marks the middle chapter of the Cenozoic Era. It is subdivided into two epochs: the Miocene and Pliocene. This period marked the further evolution and diversification of mammals, including early hominids, the ancestors of modern humans. Figure 24. Neogene Period GEOLOGIC EPOCH OF NEOGENE PERIOD i. MIOCENE EPOCH (23 MYA to 5 MYA) Earth’s Appearance: Due to continental plate movement, new mountain ranges formed during the Miocene in North America, South America, Europe, and Africa. There was continued uplift of the Himalayas and renewed uplift of the Appalachians. The polar ice cap continued to exist in Antarctica. Africa and Asia were now connected by land bridges, as were North America and Siberia. Climate: There were warmer conditions in the first half of the Miocene. In the latter 36 half of the Miocene, increased mountain building, combined with changing ocean currents and polar ice on Antarctica, led to decreased rainfall, increased seasonality, and cooler temperatures. As a result of this climate change, the forests continued to shrink in size and grasslands spread even more widely. The first true prairies appeared and covered many of the continents. Animals and Plants With increasing grasslands, hoofed mammals, with their multiple stomachs suitable for digesting the tough grasses, flourished. There were great mammal migrations from continent to continent over the land bridges. For example, elephants first migrated to North America at this time. The abundance and diversity of mammals was at its highest. The most significant event for human beings, however, was the appearance of the first anthropoid apes. The two major plant changes were the major expansion of grasslands and the appearance of kelp forests in the oceans. ii. PLIOCENE EPOCH (23 MYA to 5 MYA) Earth’s Appearance: By the beginning of the Pliocene, the continents were in very similar positions to where we find them today. The Cascade, Rocky, and Appalachian Mountains were forming, as well as the Colorado Plateau. A shift in the Caribbean Plate connected North and South America at the Isthmus of Panama, and this provided a land bridge for mammals to migrate across. The Mediterranean Sea dried out and was a grassland for several million years. The Himalayan Mountains continued to rise. Climate: The first half of the Pliocene was warmer than the world is today, and sea levels were higher. During the last half of the Pliocene, temperatures dropped, and there was less rainfall. Not only did the ice cap in Antarctica grow larger, there 37 also was an ice cap at the North Pole. Scientists still aren't sure what caused these climatic changes that eventually led to the ice age of the Pleistocene epoch. Animals and Plants Most of the plant and animal groups would be recognizable to us today, although the individual species were different. The emergence of the land bridge between North and South America in the late Pliocene made it possible for many animals to migrate into new regions. Armadillos, ground sloths, opossums, and porcupines moved into North America, and dogs, cats, bears, and horses moved into South America. Many animals became extinct because of the new competition. The modern horse evolved, and hoofed animals reached their peak on the grasslands. Early hominids in Africa evolved into several distinctly different species with only one of them surviving to the present day as modern humans. Grasslands and savannas expanded significantly due to the cooler, drier climate. The vegetation species were very similar to those of today. c. QUATERNARY PERIOD The Quaternary Period, stretching from 2.6 million years ago to the present, is the youngest chapter of the Cenozoic Era. It is subdivided into two epochs: the Pleistocene and Holocene. This period is often known as the “Ice Age” due to its signature feature: repeated cycles of glacial advance and retreat that dramatically shaped our planet. Moreover, this period is characterized by significant changes in the Earth’s climate, as well as the evolution and dispersal of modern human civilizations. Figure 25. Quaternary Period GEOLOGIC EPOCH OF QUATERNARY PERIOD i. PLEISTOCENE EPOCH (2.6 MYA to 10,000 YEARS AGO) Earth’s Appearance: 38 The position of the continents was essentially the same as it is today. However, the outline of the continents changed as a result of the ice ages. During a glacial period, sea level fell because water was trapped in the ice. During an interglacial period, sea level rose as the ice melted and the water flowed into the oceans. Climate: This was a time of global cooling and warming with ice ages and interglacial periods occurring about every 100,000 years. We are in the beginning of an interglacial period right now (as of 2020). During the glacial periods, the northern quarter of the globe was covered with ice. At its maximum, the ice was 13,000 feet thick, and sea level dropped about 430 feet. During the interglacial periods, much of the northern ice melted, and the glaciers retreated northward. The ice on Antarctica, however, which melted much less during interglacial periods, gradually increased in size. Animals and Plants Many plants and animals survived to live on the planet today, but many others did not. There was a significant number of large animals (i.e., mammoths, mastodons, saber-toothed cats, and giant ground sloths), but few of them survived. Their extinction was probably due to stresses from the fluctuating climate and being hunted by humans. By the end of the Pleistocene, modern humans had spread throughout most of the world except Antarctica. During interglacial periods, forests were dominant. When the climate cooled, grasslands expanded, and tundra dominated. ii. HOLOCENE EPOCH (10,000 YEARS AGO to PRESENT) Earth’s Appearance: Continental motions are negligible over a span of only 10,000 years—less than a kilometer. However, ice melt caused world sea levels to rise about 35 39 meters (110 ft) in the early part of the Holocene. In addition, many areas above roughly 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as 180 meters over the late Pleistocene and Holocene. Climate: Although geographic shifts in the Holocene were minor, climatic shifts were quite grand. The Holocene climatic optimum was a period of warming in which the global climate became 0.5-2°C warmer than today. It began roughly 9,000 years ago and ended about 5,000 years ago, when the earliest human civilizations in Asia and Africa were flourishing. However, the warming was probably not uniform across the world. This period of warmth ended with a cooler period with minor glaciation, which continued until about 2,000 years ago. There was a slightly warmer period from the tenth to fourteenth centuries, known as the Medieval Warm Period. This was followed by the Little Ice Age, from the thirteenth or fourteenth century to the mid nineteenth century, which was a period of significant cooling, though not as severe as previous periods during the Holocene. The Holocene warming is an interglacial period and there is no reason to believe that it represents a permanent end to the Pleistocene glaciation. It is thought that the planet could return to a new period of glaciation in as little as 3,000 years, although 19,000 years has also been posited. However, if the current global warming continues, a super-interglacial might occur, and become warmer and possibly longer than any past interglacial periods in the Pleistocene. A super- interglacial could become warmer than the Eemian Interglacial, which peaked at roughly 125,000 years ago and was warmer than the Holocene. Animals and Plants Animal and plant life have not changed much during the relatively short Holocene, but there have been major shifts in the distributions of plants and animals. The Holocene extinction event is a name customarily given to the widespread, ongoing extinction of species during the modern Holocene epoch. 40 The genera vary from mammoths to dodos, to species in the rainforest dying every year. In broad usage, the Holocene extinction event includes the remarkable disappearance of large mammals, known as megafauna, by the end of the last ice age 9,000 to 13,000 years ago. Such disappearances have been considered as either a response to climate change, a result of the proliferation of modern humans, or both. Within the past 2,000 years, a large number of species have become extinct in ways more clearly linked to human dispersal or activity. The observed rate of extinction has risen dramatically in the last 50 years. There is no general agreement on whether to consider more recent extinctions as a distinct event or merely part of a single escalating process. Only during these most recent parts of the extinction have plants also suffered large losses. Among the human activities currently considered as impacting extinctions are overhunting (either directly, or indirectly by decimation of prey populations), introduction of infectious diseases (perhaps carried by associated animals such as rats or birds), increased interspecific competition, habitat destruction, and the introduction of exotic species. Human Development Although Homo sapiens appeared during the preceding Pleistocene Epoch, and were fully differentiated as a species by the beginning of the Holocene Epoch, human societal evolution has taken place during the Holocene Epoch. Human societal and intellectual development during the Holocene Epoch produced the first species capable of significantly and consciously altering geophysical processes. Early humans developed sophisticated tools, language, and complex social structures, setting them apart from other animals. The most distinguishing aspect of the Holocene is the stable climatic conditions that differentiate it from preceding epochs. One cannot overlook the profound connection between the Holocene’s climate stability and the emergence and development of human civilization. The warm, stable conditions allowed humans to transition from nomadic hunter-gatherers to settled agricultural societies. The end of the Ice Age brought a period of increased rainfall in the Fertile Crescent, leading to abundant 41 growth of wild cereals. This served as a catalyst for the development of agriculture. With agriculture came settled life, leading to the establishment of the first cities and civilizations, notably in Mesopotamia, Egypt, Indus Valley, and China. Human influence on the Earth’s ecosystem has been so significant during the Holocene that many scientists believe we have entered a new epoch: the Anthropocene. Human activities such as deforestation, agriculture, urbanization, and industrialization have extensively modified the landscape and altered the global carbon cycle. III. Earth's Timeline and Geological Events 4.6 Billion Years Ago (Earth’s Formation) Earth’s geological history spans over 4.6 billion years, beginning with its formation from a cloud of dust and gas. Initially, Earth was covered in molten lava, rendering it uninhabitable. During this time, heavy elements like iron sank to form its core, while lighter elements coalesced to create the crust. A significant event was the formation of the moon, which stabilized Earth’s tilt and rotation, allowing for the development of seasons. 4.0 – 2.5 Billion Years Ago (Cooling and Primitive Life) As Earth cooled, water vapor condensed to form oceans, leading to a more stable climate. Early life forms, particularly cyanobacteria, emerged in these oceans. These organisms played a crucial role by converting sunlight into energy and releasing oxygen as a byproduct, triggering the Great Oxygenation Event. This event caused the extinction of many anaerobic life forms and paved the way for the evolution of more complex aerobic organisms. 541 – 245 Million Years Ago (The Cambrian Explosion and Fossil Records) The Cambrian Explosion, around 541 million years ago, marked a dramatic diversification of life, resulting in the emergence of hard-shelled invertebrates, fish, and eventually amphibians. This period laid the foundation for future life forms. However, the end of 42 the Paleozoic Era witnessed the largest extinction event in Earth’s history, eliminating a significant percentage of marine and terrestrial species. 245 – 66 Million Years Ago (The Age of Reptiles and Dinosaurs) During the Mesozoic Era, reptiles thrived, and dinosaurs became the dominant terrestrial vertebrates for approximately 160 million years. This era saw the existence of Pangea, a supercontinent, which gradually broke apart due to plate tectonics. The diversity of dinosaurs and their ecological adaptations reflected a complex and dynamic environment. 66 Million Years Ago – Present (The Age of Mammals and Homo Sapiens) The catastrophic extinction event caused by a massive asteroid impact 66 million years ago led to the demise of dinosaurs, marking the transition to the Age of Mammals. With dinosaurs gone, mammals began to evolve and diversify. Eventually, early hominids emerged, leading to the rise of modern humans. This timeline illustrates the remarkable journey of Earth’s history and the evolution of life over billions of years. IV. Applications of the Geological Time Scale in Earthquake Engineering The Geologic Time Scale is a crucial tool for understanding the history of the Earth and the evolution of life on our planet. It has a wide range of applications in various fields, including geology, paleontology, biology, archaeology, and more. Some of the most important applications of the Geologic Time Scale are: a. Age Dating of Rocks and Fossils The Geologic Time Scale is used to determine the age of rocks, fossils, and other geological formations. This is essential for understanding the evolution of life on Earth and for reconstructing past environments and ecosystems. b. Correlation of Rock Strata The Geologic Time Scale is used to correlate rock strata across different geographic regions. This allows geologists to reconstruct the Earth’s history and to understand the relationships between different geological events. 43 c. Resource Exploration The Geologic Time Scale is used by the petroleum, mineral, and mining industries to explore and extract natural resources. A knowledge of the age and depositional environment of rocks can be used to identify potential resource-rich areas. d. Climate Change Studies The Geologic Time Scale is used to study climate change over long periods. By analyzing rocks, fossils, and other geological formations, scientists can reconstruct past climate conditions and understand the mechanisms and causes of climate change. Advances in field observation, laboratory techniques, and numerical modeling allow geoscientists to show, with increasing confidence, how and why climate has changed in the past. e. Evolutionary Biology Evolutionary biologists use the Geologic Time Scale to comprehend the development of life on Earth. It offers a framework for understanding interspecies connections and reconstructing the evolutionary history of various groupings of animals. f. Archaeology Archaeologists use the Geologic Time Scale to determine the age of archaeological sites and artifacts. Understanding how human civilizations have evolved and reconstructing earlier cultural and technical systems depend on this. V. Limitations and Criticisms of the Geological Time Scale a. Incomplete Fossil Record The GTS is based on the principle of relative dating, which relies on the sequence of rock layers and the fossils they contain. Fossils are not always preserved, and there are gaps in the fossil record, making it difficult to establish precise dates for some events or organisms. Many life forms may not have left behind fossils, leading to incomplete knowledge of Earth's biotic history. 44 b. Assumptions About Rates of Change The Geologic Time Scale (GTS) is indeed based on certain assumptions about the rates of geological and biological processes. These assumptions can be challenged, revised, and refined as new data, techniques, and scientific understanding become available. This process of refinement is an essential aspect of the scientific method and helps ensure that the GTS remains an accurate and up-to-date representation of Earth's history. c. Dating Techniques Absolute dating methods, such as radiometric dating, are used to assign numerical ages to certain rocks and minerals. While these methods are powerful, they are not always applicable, and they come with their own sources of error and uncertainty. d. Conflicting Interpretations Different scientists can have conflicting interpretations of the same data, leading to different models of the Geologic Time Scale. This can result in disagreements about the timing of events and the relationships between different species and geological formations. e. Controversies The Geologic Time Scale is not immune to controversies, and different interpretations of data can lead to debates and disagreements about the history of the Earth and the evolution of life. For example, there have been controversies surrounding the timing of mass extinctions and the origins of different groups of organisms. 45 References: Berggren, W. A. (n.d.). Cenozoic Era. Encyclopædia Britannica. https://www.britannica.com/science/Cenozoic-Era Cenozoic. Cenozoic | U.S. Geological Survey. (n.d.). https://www.usgs.gov/youth-and-education- in-science/cenozoic Charles. (2017, March 10). Proterozoic earth – The first animals. Earthly Universe. https://earthlyuniverse.com/proterozoic-earth-first-animals/ Earthhow. (2023, September 23). What is Earth’s Geological Time Scale? Earth How. https://earthhow.com/earth-geological-time-scale/ Earthhow. (2024, March 29). Earth Timeline: A Guide to Earth’s Geological History and Events [Infographic]. Earth How. https://earthhow.com/earth-timeline-geological-history-events/ Geologic Time Scale - Geology (U.S. National Park Service). (n.d.). https://www.nps.gov/subjects/geology/time-scale.htm Geological time scale. (2021, September 13). Digital Atlas of Ancient Life. https://www.digitalatlasofancientlife.org/learn/geological-time/geological-time-scale/ 46 Holocene. New World Encyclopedia. (n.d.). https://www.newworldencyclopedia.org/entry/Holocene Phanerozoic. (2022, October 8). https://encyclopedia.pub/entry/28402 Professor Dave Explains. (2022, March 18). History of the Earth Part 1: Hadean, Archean, and Proterozoic Eons [Video]. YouTube. https://www.youtube.com/watch?v=DWC2lZHaq5c Rafferty, J. P. (2024, August 27). Hadean Eon | Start, Timeline, & Facts. Encyclopedia Britannica. https://www.britannica.com/science/Hadean-Eon Sekscinska, A. (2021, August 17). Archean And Hadean Eons. The Secrets Of The Universe. https://www.secretsofuniverse.in/history-of-life-2-archean/ South Carolina Department of Natural Resources - Geology Section. (2005). Geologic Time and Earth’s Biological History. https://www.dnr.sc.gov/geology/pdfs/education/Geologic%20Time.pdf The Editors of Encyclopaedia Britannica. (2024, September 13). Geologic time | Periods, Time Scale, & Facts. Encyclopedia Britannica. https://www.britannica.com/science/geologic-time Windley, B. F. (1998a, July 20). Archean Eon | Atmosphere, Timeline, and Facts. Encyclopedia Britannica. https://www.britannica.com/science/Archean-Eon Windley, B. F. (1998b, July 20). Proterozoic Eon | Oxygen Crisis, Animals, & Facts. Encyclopedia Britannica. https://www.britannica.com/science/Proterozoic-Eon Zimmermann, K. A. (2016, June 9). Cenozoic era: Facts about climate, Animals & Plants. LiveScience. https://www.livescience.com/40352-cenozoic-era.html 47 TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES Ayala Blvd., Ermita, Manila, 1000, Philippines Tel No. +632-301-3001 local 102 | Fax No. +632-521-4063 Email: [email protected] | Website: www.tup.edu.ph PROCESSIONAL COURSE – SPECIALIZED 2 PCS2 - M GROUP PRESENTATION EARTH STRUCTURES AND PLATE TECTONICS SUBMITTED BY: Group No. 03 Aganan, Je-Ann R. Andao, Christian Cantre, Leonardo Jr. B. Loraña, Earl Donde K. Yanzon, Annielle Joy A. BSCE – 4C SUBMITTED TO: ENGR. EDMUNDO C. DELA CRUZ 48 1. EARTH STRUCTURE The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. Each layer has a unique chemical composition, physical state, and can impact life on Earth's surface. Earth's Crust “Crust” describes the outermost shell of a terrestrial planet. Crust is composed of solid rocks, mostly basalt and granite Earth's crust is generally divided into older, thicker continental crust and younger, denser oceanic crust. It is the thinnest layer ranging from about 5 km to 70 km and thickness. o Continental Crust The continental crust is the thicker layer of the Earth’s crust that is found under the continents. o Oceanic Crust The oceanic crust is the thinner layer of the Earth’s crust that is found under the ocean basins. o Mohorovicic Discontinuity (Moho) boundary of crust and mantle. The Moho does not exist at a uniform depth, because not all regions of Earth are equally balanced in isostatic equilibrium. Isostasy describes the physical, chemical, and mechanical differences that allow the crust to “float” on the sometimes more malleable mantle. The Moho is found at about eight kilometers (five miles) beneath the ocean and about 32 kilometers (20 miles) beneath continents. Mantle The mantle is the mostly solid bulk of Earth's interior. The mantle lies between Earth's dense, super- heated core and its thin outer layer, the crust. The mantle is about 2,900 kilometers (1,802 miles) thick and makes up a whopping 84 percent of Earth’s total volume. o Upper Mantle The upper mantle is relatively rigid and contains the asthenosphere, a semi-fluid layer that allows the movement of tectonic plates. 49 Two parts of the upper mantle are often recognized as distinct regions in Earth’s interior: the lithosphere and the asthenosphere. o Lithosphere The lithosphere is the solid, outer part of Earth, extending to a depth of about 100 kilometers (62 miles). The lithosphere includes both the crust and the brittle upper portion of the mantle. The lithosphere is both the coolest and the most rigid of Earth’s layers. o Asthenosphere The asthenosphere is the denser, weaker layer beneath the lithospheric mantle. It lies between about 100 kilometers (62 miles) and 410 kilometers (255 miles) beneath Earth’s surface. The temperature and pressure of the asthenosphere are so high that rocks soften and partly melt, becoming semi-molten. o Lower Mantle The solid lower mantle contributes to the overall convection and heat transfer within the Earth’s interior. The Outer Core The outer core extends from 2,900 km to about 5,150 km beneath the Earth’s surface. It mainly consists of liquid iron and nickel. The motion within this layer generates the Earth’s magnetic field. The Inner Core The inner core is the central part of the Earth. It extends from a depth of about 5,150 km to the Earth’s center at about 6,371 km. Although it is very hot, the inner core is solid due to the immense pressure at this depth. It’s composed primarily of iron, with minor amounts of nickel and other lighter elements. 2. PLATE TECTONIC AND MOVEMENT Plate Tectonics, theory dealing with the dynamics of Earth’s outer shell—the lithosphere—that revolutionized Earth sciences by providing a uniform context for understanding mountain-building processes, volcanoes, and earthquakes as well as the evolution of Earth’s surface and reconstructing its past continents and oceans. The concept of plate tectonics was formulated in the 1960s. According to the theory, Earth has a rigid outer layer, known as the lithosphere, which is typically about 100 km (60 miles) thick and overlies a plastic (moldable, partially molten) layer called the asthenosphere. The lithosphere is broken up into seven very large continental- and ocean-sized plates, six or seven medium-sized regional plates, and several small ones. These plates move relative to each other, typically at rates of 5 to 10 cm (2 to 4 inches) per year, and interact along their boundaries, where they converge, diverge, or slip past one another. Such interactions are thought to be responsible for most of Earth’s seismic and volcanic activity, although earthquakes and volcanoes can occur in plate interiors. 50 Supercontinents Pannotia (633-573 mya) A short-lived supercontinent, centered around the south pole, was Pannotia. Modern- day Africa was at the center of Pannotia. Apparently, the scientific jury is still out on whether Pannotia actually existed. Pannotia existed during the very end of the Neoproterozoic period. Life during this period was pretty basic. Shelled organisms didn’t exist but some kinds of worms did. We don’t have too many fossils from this period and prior to it. Gondwana – the miniature supercontinent (550-150 mya) Gondwana was a supercontinent that existed from about 550 to 180 million years ago. It was formed when several smaller continents, including what is now South America, Africa, India, Australia, and Antarctica, collided and merged together. The name “Gondwana” originates from the Gondwana region of central India. Rocks from the Late Paleozoic and Early Mesozoic eras are exposed there. Scientists believe that these rocks are remnants of the ancient Gondwanan continent. Pangea (336-175 mya) Pangea (sometimes spelled pangaea) was Earth’s most recent supercontinent. This supercontinent contained nearly all the land on Earth. This fact is reflected in Pangea’s name which means ‘all lands’ in Greek. In total, the single continent of Pangea took up about 1/3 of Earth’s surface. The other two-thirds of the Earth was a single ocean, named Panthalassa. Plate Movement cause mountains to rise where plates push together, or 51 converge, and continents to fracture and oceans to form where plates pull apart or diverge. The continents are embedded in the plates and drift passively with them, which over millions of years results in significant changes in Earth’s geography. Alfred Wegener (1888 – 1930) Wegener first presented his theory in lectures in 1912 and published it in full in 1915 in his most important work, Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He searched the scientific literature for geological and paleontological evidence that would buttress his theory, and he was able to point to many closely related fossil organisms and similar rock strata that occurred on widely separated continents, particularly those found in both the Americas and in Africa. 4 Mechanisms Why Tectonic Plates Moved Apart Over Time Mantle Convection - describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere. The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time. Ridge Push - is one of the main driving forces of plate tectonics. It refers to the pushing force that plates experience as they slide down the raised asthenosphere underneath Mid Ocean Ridges. Slab Pull - is the pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight. Slab Suction - is one of the forces that drive plate tectonics. It creates a force that pulls down plates as they are subducting and speeds up their movement, creating larger amounts of displacement. 52 3. PLATE BOUNDARIES A plate boundary is a three-dimensional surface or zone across which there is a significant change in the velocity (speed or direction) of motion of one lithospheric plate relative to the adjacent lithospheric plate. Three types of Plate Boundary: Convergent Boundary Divergent Boundary Transform Boundary 1. DIVERGENT BOUNDARY o A t d i v e r g e n t boundaries, plates move away from each other. This movement results in the creation of new crust as magma rises from the mantle, solidifies, and forms new oceanic crust. o Divergent boundaries are responsible for the continuous reshaping and formation of earth’s crust. o An example of a divergent boundary in the Philippines is the **Philippine Rise** area, particularly in the context of the **Mindoro and Palawan regions**. While the Philippines is primarily characterized by convergent and transform boundaries, the Philippine Rise (formerly known as the Benham Rise) represents a zone where the oceanic crust is being created as tectonic plates pull apart. o Another example is the **Sulu Sea**, which shows signs of rifting and divergence between the Philippine Sea Plate and the smaller plates in that region. However, divergent activity is less prominent in the Philippines compared to its convergent boundaries. 53 2. CONVERGENT BOUNDARY o C o n v e r g e n t boundaries are places where tectonic plates collide or come together. When two plates meet, their interactions can result in various geological phenomena. o It contribute to the formation of mountains, volcanic activity, and earthquakes. o An example of a convergent boundary in the Philippines is the **Manila Trench**. Here, the **Philippine Sea Plate** is subducting beneath the **Eurasian Plate**. This subduction zone is associated with significant geological activity, including the formation of volcanoes, earthquakes, and the development of deep-sea trenches. Other notable features related to this convergent boundary include the **Bataan Peninsula** and the volcanic arcs like the **Zambales Mountain Range**. Three styles of convergent plate boundaries: CONTINENTAL-CONTINENTAL CONVERGENCE o In this scenario, two continental plates collide. Since both plates are less dense than the mantle, neither is subducted. Instead, they crumple and fold, leading to the formation of large mountain ranges (like the Himalayas, which formed from the collision of the Indian and Eurasian plates). OCEANIC-OCEANIC CONVERGENCE o When two oceanic plates collide, one plate is usually subducted under the other. This process creates deep ocean trenches (like the Mariana Trench) and volcanic island arcs (such as the Aleutian Islands). OCEANIC-CONTINENTAL CONVERGENCE o This occurs when an oceanic plate collides with a continental 54 plate. The denser oceanic plate is subducted beneath the continental plate, leading to the formation of a trench (like the Peru Trench) and volcanic arcs (such as the Andes Mo

Geological Time Scale Written Report - Technological University of the Philippines - Manila

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