History of Life on Earth PDF

History of life on earth An Introduction to Geologic Time Scale  Activity 2 In a long bond paper, make your own timeline (Geological Time Scale) on the history of life on Earth which includes the 4 divisions; Eons, Era, Periods, Epoch. Include the significant events that ha...

History of life on earth An Introduction to Geologic Time Scale  Activity 2 In a long bond paper, make your own timeline (Geological Time Scale) on the history of life on Earth which includes the 4 divisions; Eons, Era, Periods, Epoch. Include the significant events that happened in the specific periods and the different life forms existed during those times. -Individual work  Lesson Objectives At the end of the lesson, you should be able to: Describe general features of the history of life on Earth, including generally accepted dates and sequence of the geologic time scale and characteristics of major groups of organisms present during these time periods  Discussion 01 03 Introduction Eras An introduction to the concept of Geologic A discussion of the eras under the Time Scale, including its definition and Phanerozoic Eon, namely the Paleozoic, significance in earth history Mesozoic, and Cenozoic eras 02 04 Eons Periods A discussion of the important eons in the A discussion of the numerous periods of the time scale: Precambrian (Hadean, Archean, three major geological eras and Proterozoic) and Phanerozoic Introduction What is Geologic Time Scale? The geologic time scale distinguishes Earth's history based on life-forms that existed at certain times since the planet's formation. The majority of these life forms are discovered as fossils, which are the remains or evidence of an organism from the geologic past that have been preserved in silt or rock. Without fossils, geologists might not have established that the world has a past that predates humanity.  What is Geologic Time Scale? While studying the physical geology and history of the planet earth, it is necessary to know about the Geological Time Scale, in detail. The study of the geological time scale is necessary to every student of earth, atmospheric and all life sciences. The origin and evolution of the Earth took place over a period of billions of years. The evolution of life on earth is also a part of that prolonged Earth's history. It is a fact that the planet earth has evolved as one of the planets from the common nebulae.  What is Geologic Time Scale? Due to this reason, the age of the earth is also related to the age of the Solar System. From the Big-Bang theory, till today, the time span or time- frame of the Earth's evolution is very extensive. The periods of remarkable development in the evolution of life, the stages in the evolution of continents, the stages in the evolution of ocean basins, the origin and evolution of life on earth, and their proliferations or mass- extinctions, are represented in the form of geological records on the surface rocks and sediments all, over the world. They clearly show the fossilized evidences of the past life and environment.  Geologic Time Scale Era Period Next to longest subdivision; Based on types of life marked by major changes existing at the time in the fossil record Eon Epoch Longest subdivision; based Shortest subdivision; marked on the abundance of by differences in life forms certain fossils and can vary from continent to continent. How GTS was constructed The Geological Time Scale was constructed using the evidences collected from various sources, like Field observations Fossil records Stratigraphic correlations How GTS was constructed Radioactive dating Paleomagnetic orientations Orbital revolution pattern of the Earth and The duration of the daily rotation of the earth around its axis. Paleomagnetic sampling in Norway. Credit: Daniel Pastor-Galán How GTS was constructed Some of the major events like mass extinctions, appearance of new species or genera of life, mountain-building movements drifting of continents spreading of ocean floors widespread glaciations dominance of certain species massive migration of life between land and water are all considered while accounting the geologic time scale.  History of earth The changes that occurred throughout the history of the earth stand well in the form of distinct and contrasted features. They all have shown orderly and uniform operation of natural systems, in the past. The early history of the earth differs in character from late history. Due to this reason, there was a need to divide the units of time in terms of billions of years or millions of years.  History of earth The early history of the planet is described in billion-year units of time. The late history of the earth is described in million-year units of time. And finally, the recent time is described in 1000's of year units. Several experts attempted to reconstruct the schedule of events of profound changes that happened at various stages by considering the aspects of the earth's physical systems. The geological time scale was formulated with care for universal application. What is the origin of the geologic time scale? The first people who needed to understand the geological relationships of different rock units were miners. Mining had been of commercial interest since at least the days of the Romans, but it wasn't until the 1500s and 1600s that these efforts produced an interest in local rock relationships. What is the origin of the 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:  What is the origin of the geologic time scale? 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. These important principles have formed the framework for the geologic area of stratigraphy, which is the study of layered rock (strata). What is the origin of the geologic time scale? What is the origin of the geologic time scale? James Hutton, a Scottish physician and geologist (1726-1797), thought the surface of the earth was an ever-changing environment explained by what can be seen to be This theory was called which was later catch-phrased as What is the origin of the geologic time scale? William Smith - a surveyor, canal builder, and amateur geologist from England. In 1815 Smith produced a geologic map of England in which he successfully demonstrated the validity of the principle of faunal succession. This principle simply stated that fossils are found in rocks in a very definite order. This principle led others that followed to use fossils to define increments within a relative time scale. What is the origin of the geologic time scale? The principle of biologic succession: Each age in the history is unique such that fossil remains will be unique. This permits vertical and horizontal correlation of the rock layers based on fossil species  SEATWORK Answer the following questions: 1. How old is the Earth? 2. What is the biggest time frame in the GTS? 3. What is the smallest time frame in the GTS? 4. What are mass extinctions? How many mass extinctions events happened in the GTS?  SEATWORK Answer the following questions: 1. The Earth has an incredibly long history. How does understanding of geologic time and the significant geologic events of the past impact your understanding of unique responsibility and place on earth? 2. How does understanding the past help us understand the present?  Precambrian Eon More than 85% of earth's history falls under this supereon, from 4.6 billionyears ago to 540 million years ago. Hadean Eon (4.6 Billion Years ago) The solidification of the earth's continental and oceanic crust Archean Eon (4 Billion Years ago) The evolution of earth's first life forms Proterozoic Eon (2.5 Billion Years ago) The appearance of multi-celled animals and the gathering of land masses to form continents  Precambrian Eon Hadean Eon (4.6 Billion Years ago to 4 billion years ago) The solidification of the earth's continental and oceanic crust During Hadean time, the solar system was forming within a cloud of dust and gas known as the solar nebula, which eventually spawned asteroids, comets, moons and planets It was characterized by Earth's formation and it's hellish environment Photo by: Cesar Alcaraz  Precambrian Eon Archean Eon (4 Billion Years to 2.5 billion years ago) The evolution of earth's first life forms Approximately 70 percent of continental landmass was formed during this time. Earth had acquired enough mass to hold a reducing atmosphere composed of methane, ammonia and other gases. Water from comets and hydrated minerals condensed in the atmosphere and fell as torrential rain, cooling the planet and filling the first oceans with liquid water. It is probable that these microscopic prokaryotes began as chemoautotrophs, anaerobic bacteria able to obtain carbon from carbon dioxide (CO2). By the end of the Archean, the ocean floor was covered in a living mat of bacterial life.  Precambrian Eon Proterozoic Eon (2.5 Billion Years ago) The appearance of multi-celled animals and the gathering of land masses to form continents About 2.5 billion years ago, enough shield rock had formed to start recognizable geologic processes such as plate tectonics. About 1.2 billion years ago, plate tectonics forced the available shield rock to collide, forming Rodinia. coastal waters were filled with rounded colonies of photosynthetic algae known as stromatolites  Precambrian Eon Proterozoic Eon (2.5 Billion Years ago) The appearance of multi-celled animals and the gathering of land masses to form continents The Ediacaran Period , the last of the Proterozoic Era, saw the first multicellular organisms. Autotrophs and soft-bodied heterotrophs filled the continental shelf regions around Rodinia 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. Sponges lacking organs or a nervous system, they lived by drawing water through their bodies and filtering out food particles Annelids or segmented flatworms, had fluid-filled body cavities and breathed through their skins.  Sea anemone Sponges  Precambrian Eon Proterozoic Eon (2.5 Billion Years ago) The appearance of multi-celled animals and the gathering of land masses to form continents  Phanerozoic Eon Cenozoic Era (65 Million Years ago - Now This is the most recent among the eras of the Phanerozoic Era; this era marks the age of mammals and the first human evolution. Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms life, called the Cambrian Explosion. Marine trilobites were common. The first invertebrates and fish are found, later the first amphibians and insects. Diverse land plants develop and coal swamps form in certain areas. The first reptiles form. This era ended with the massive Permian Extinction, wiping out many successful species Paleozoic Era (544 Million Years Ago) Permian Period (298.9 MYA) Pennsylvanian Period (323.2 MYA) Mississippian Period (358.9 MYA) Devonian Period (419.2 MYA) Silurian Period (443.8 MYA) Ordovician Period (485.4 MYA) Cambrian Period (541.0 MYA)  LIFE IN Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms The Paleozoic began with the Cambrian Period, 53 million years best known for ushering in an explosion of life on Earth. This "Cambrian explosion" included the evolution of arthropods (ancestors of today's insects and crustaceans) and chordates (animals with rudimentary spinal cords).  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms In the Paleozoic Era, life flourished in the seas. After the Cambrian Period came the 45- million-year Ordovician Period, which is marked in the fossil record by an abundance of marine invertebrates. Perhaps the most famous of these invertebrates was the trilobite, an armored arthropod that scuttled around the seafloor for about 270 million years before going extinct.  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms After the Ordovician Period came the Silurian Period (443.8 million to 419.2 million years ago), which saw the spread of jawless fish throughout the seas. Mollusks and corals also thrived in the oceans, but the big news was what was happening on land: the first Ostracoderm: Ostracoderms were some of the earliest jawless fishes and were covered in bony armor. undisputed evidence of terrestrial life. Present-day jawless fishes lack bone in their scales. Hagfishes: Pacific hagfish are scavengers that live on the ocean floor. These agnathans are classified as Myxini and do not have a vertebral column.  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms This was the time when plants evolved, though they most likely did not yet have leaves or the vascular tissue that allows modern plants to siphon up water and nutrients. Those developments would appear in the Devonian Period, the next geological period of the Paleozoic. Ferns appeared, as did the first trees. At the same time, the first vertebrates were colonizing the land. These vertebrates were called tetrapods, and they were widely diverse: Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms The Carboniferous Period, which lasted from about 359 million years ago to 299 million years ago, answered the question, "Which came first the chicken or the egg?" definitively. Long before birds evolved, tetrapods began laying eggs on land for the first time during this period, allowing them to break away from an amphibious lifestyle. Trilobites were fading as fish became more diverse. The ancestors of conifers appeared, and dragonflies ruled the skies..  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms Tetrapods were becoming more specialized, and two new groups of animals evolved. The first were marine reptiles, including lizards and snakes. The second were the archosaurs, which would give rise to crocodiles, dinosaurs and birds. Most creepily, this era is sometimes referred to as the "Age of the Cockroaches," because roaches' ancient ancestor (Archimylacris eggintoni) was found all across the globe during the Carboniferous. This map is called a cladogram, and this particular cladogram shows the relationships among the archosaurs. https://ucmp.berkeley.edu/diapsids/archosy.html Broadly speaking there two types of archosaur: 1. Those more closely related to birds (bird-line) called the ornithodirans, which includes dinosaurs and pterosaurs. 2. And those more closely related to crocodiles (crocodile- line) called the pseudosuchians, which are less popularly known. Photo source: https://dawndinos.com/overview/  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms The last period of the Paleozoic was the Permian Period, which began 298.9 million years ago and wrapped up 251.9 million years ago. This period would end with the largest mass extinction ever: the Permian extinction. Before the Permian mass extinction, though, the warm seas teemed with life. Coral reefs flourished, providing shelter for fish and shelled creatures, such as nautiloids and ammonoids. Modern conifers and ginkgo trees evolved on land. Terrestrial vertebrates evolved to become herbivores, taking advantage of the new plant life that had colonized the land. Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms UCMP Berkeley  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms The Permian extinction was characterized by the elimination of about 90 percent of the species on Earth, which included more than 95 percent of the marine species and 70 percent of the terrestrial species. In addition, more than half of all taxonomic families present at the time disappeared. This event ranks first in severity of the five major extinction episodes that span geologic time.  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms The Permian extinction was not restricted to marine invertebrates. Several groups of aquatic vertebrates, such as the acanthodians, thought to be the earliest jawed fishes, and the placoderms, a group of jawed fishes with significant armour, were also eliminated. Notable terrestrial groups, such as the pelycosaurs (fin-backed reptiles), Moschops (a massive mammal-like reptile), and numerous families of insects also met their demise. In addition, a number of groups (such as sharks, bony fishes, brachiopods, bryozoans, ammonoids, therapsids, reptiles, and amphibians) experienced significant declines by the end of the Permian Period.  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms Causes of Permian extinction 1. Temperature crises 2. Alteration of the carbon cycle 3. Population explosion of methane-producing microbes Other possible causes assembly of Pangea, a vast north-south supercontinent  Paleozoic geology and climate All this evolution took place against the backdrop of shifting continents and a changing climate. During the Cambrian Period of the Paleozoic, the continents underwent a change. They had been joined as one supercontinent, Rodinia, but during the Cambrian Period, Rodinia fragmented into Gondwana (consisting of what would eventually become the modern continents of the Southern Hemisphere) and smaller continents made up of bits and pieces of the land that would eventually make up today's northern continents.  Paleozoic geology and climate The Cambrian was warm worldwide, but would be followed by an ice age in the Ordovician, which caused glaciers to form, sending sea levels downward. Gondwana moved further south during the Ordovician, while the smaller continents started to move closer together. In the Silurian Period, the land masses that would become North America, central and northern Europe, and western Europe moved even closer together. Sea levels rose again, creating shallow inland seas.  Paleozoic geology and climate In the Devonian, the northern land masses continued merging, and they finally joined together into the supercontinent Euramerica. Gondwana still existed, but the rest of the planet was ocean. By the last period of the Paleozoic, the Permian, Euramerica and Gondwana became one, forming perhaps the most famous supercontinent of them all: Pangaea. The giant ocean surrounding Pangaea was called Panthalassa. Pangaea's interior was likely very dry, because its massive size prevented water-bearing rain clouds from penetrating far beyond the coasts. Mesozoic Era (245 Million Years Ago) Cretaceous Period (145.0 MYA) Jurassic Period (201.3 MYA) Triassic Period (251.9 MYA)  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. The Mesozoic era saw the rise of some of the most iconic animals, from Tyrannosaurus rex to birds and mammals.  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. During the Mesozoic, or "Middle Life" era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth. The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles or the age of dinosaurs.  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. LIFE AND CLIMATE Life slowly rebounded, eventually giving way to a flourishing diversity of animals, from massive lizards to monstrous dinosaurs. The Triassic period, from 252 million to 200 million years ago, saw the rise of reptiles and the first dinosaurs. The Jurassic period, from about 200 million to 145 million years ago, ushered in birds and mammals  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction.  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. Scientists have unveiled stunning fossils of an ancient seaborne "dragon" discovered in China. The 240 million-year-old animal nicknamed the "Chinese dragon" belongs to the species Dinocephalosaurus orientalis, a reptile that used its remarkably long neck to ambush unsuspecting prey in shallow waters during the Triassic period (252 million to 201 million years ago). The species was first found in limestone deposits in southern China in 2003, but scientists have now pieced together remains to reconstruct the full 16.8-foot (5 meters) span of the spectacular ancient carnivore for the first time.  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. And the Cretaceous period, from 145 million to 66 million years ago is known for its iconic dinosaurs, such as Triceratops, and pterosaurs such as Pteranodon. Coniferous plants, or those that have cone-bearing seeds, already existed at the beginning of the era, but they became much more abundant during the Mesozoic. Flowering plants emerged during the late Cretaceous period. The lush plant life during the Mesozoic era provided plenty of food, allowing the biggest of the dinosaurs, such as the Argentinosaurus, to grow up to 80 tons  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. Extinctions At the end of the Triassic period, roughly 201 million years ago, most amphibious creatures and crocodile-like creatures that lived in the tropics were wiped out. Because the fossil record is incomplete, it's difficult to say exactly what caused the extinctions, or even how rapidly they occurred. After all, certain species or traces of catastrophic events could be missing in the fossil record simply because the sediments may have disappeared over tens of millions of years.  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. However, there are a few prime suspects in each of the extinctions. At the end of the Permian, the Siberian Traps underwent massive volcanic eruptions, which most geologists believe caused the world's biggest extinction. Exactly how, however, is up for debate. Most scientists agree that an asteroid impact wiped out the dinosaurs at the end of the Cretaceous period. The impact would have kicked up so much dust that it blocked the sun, halted photosynthesis, and led to such a huge disruption in the food chain that everything that wasn't a scavenger or very small died.  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction. But the Deccan Traps, in what is now India, were spewing massive amounts of lava both before and after the asteroid impact, and a few scientists believe these flows either directly caused or accelerated the dinosaurs' demise.  Holocene Period (0.01 MYA) Cenozoic Era (65 Million Years ago Pleistocene Period (2.6 MYA) Pliocene Period (5.3 MYA) Miocene Period (23.0 MYA) Oligocene Period (33.9 MYA) Eocene Period (56.0 MYA) Paleocene Period (66.0 MYA)  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop Paleogene period (65-23 million years ago), which consists of the Paleocene, Eocene and Oligocene epochs); Neogene period (23-2.6 million years ago), which includes the Miocene and Pliocene epochs); Quaternary period (2.6 million years ago to the present), consisting of the Pleistocene and Holocene epochs). While it is widely accepted that we are still in the Holocene epoch, some scientists argue that we have entered the Anthropocene epoch.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The Cenozoic era began about 65 million years ago and continues into the present. The Cenozoic era, which began about 65 million years ago and continues into the present, is the third documented era in the history of Earth. The current locations of the continents and their modern-day inhabitants, including humans, can be traced to this period. The era began on a big down note, catching the tail end of the Cretaceous-Paleogene extinction event at the close of the Cretaceous period that wiped out the remaining non-avian dinosaurs.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The term Cenozoic, first spelled "Kainozoic," was originally used in an 1840 entry in the Penny Cyclopedia encyclopedia in an article written by British geologist John Phillips. The name is derived from the Greek phrase meaning life. The beginning of the Paleogene period was a time for the mammals that survived from the Cretaceous period. Later in this period, rodents and small horses, such as Hyracotherium, are common and rhinoceroses and elephants appear. As the period ends, dogs, cats and pigs become commonplace. Other than a few birds that were classified as dinosaurs, most notable the Titanis, the dinosaurs were gone. Large flightless birds, such as the Diatryma, thrived.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop Climate and geography The global climate of the early portion of the Cenozoic period was much warmer than it is today, and the overall climate of the Earth was much more consistent regardless of proximity to the equator. The most significant period of global warming, known as the Paleocene Eocene Thermal Maximum, took place of 55.8 million years ago. It was followed by a long cool, dry period. The current global warming event has been set off primarily by human activity. Each segment of the Cenozoic experienced different climates. During the Paleogene period, most of the climate was tropical. The Neogene period saw a drastic cooling, which continued into the Pleistocene epoch of the Quaternary period.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop As for the changing landscape, the continents drifted apart during the Paleogene period, creating vast stretches of oceans. This had a significant impact on the climate and marine life surrounding each continent. During the Pleistocene epoch, glaciers covered central North America, extending as far east as New York, south to Kansas and Nebraska and west to the northern West Coast. The Great Lakes were formed as the glaciers receded. Several of the foremost mountain ranges, including the Alps, Himalayas and the Rocky Mountains, were formed during the Cenozoic era.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop Life during the Cenozoic Era The Cenozoic era is also known as the Age of Mammals because the extinction of many groups of giant mammals, allowing smaller species to thrive and diversify because their predators no longer existed. Due to the large span of time covered by the period, it is beneficial to discuss the animal population by the milestone of the era rather than in generalities.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The beginning of the Paleogene period was a time for the mammals that survived from the Cretaceous period. Later in this period, rodents and small horses, such as Hyracotherium, are common and rhinoceroses and elephants appear. As the period ends, dogs, cats and pigs become commonplace. Other than a few birds that were classified as dinosaurs, most notable the Titanis, the dinosaurs were gone. Large flightless birds, such as the Diatryma, thrived.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The Neogene period gives rise to early primates, including early humans. Bovids, including cattle, sheep, goats, antelope and gazelle, flourish during this period. Cave lions, sabre-toothed cats, cave bears, giant deer, woolly rhinoceroses, and woolly mammoths were prevailing species of the Quaternary period. Without the dinosaurs, plant life had an opportunity to flourish during the Cenozoic era. Nearly every plant living today had its roots in the Cenozoic era. During the early part of the era, forests overran most of North America. However, as the climate cooled forests died off, creating open land.  Cenozoic Era (65 Million Years ago Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop Due to the widening of the oceans, sharks, whales and other marine life proliferated. The Great Lakes that formed in the western United States during the Eocene epoch were the perfect home for bass, trout and other fresh-water species. As the forests thinned, grasses began to spread out over the plains of North America and savannas covered the land in the middle of the continent. Among the common plant life were pines, mosses, oaks and grasses. Flowering plants and edible crops dominate the landscape in the later part of this era as humans cultivate the land.  Pleistocene epoch: The last ice age Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The Pleistocene featured ice age giants and the arrival of modern humans. The Pleistocene epoch is a geological time period that includes the last ice age, when glaciers covered huge parts of the globe. Also called the Pleistocene era, or simply the Pleistocene, this epoch began about 2.6 million years ago and ended 11,700 years ago Modern humans, or Homo sapiens, evolved during the Pleistocene and spread across most of Earth before the period ended The epoch also featured ice age giants, such as woolly mammoths (Mammuthus primigenius) and saber-toothed cats, many of which disappeared at the end of the Pleistocene in a major extinction event.  Holocene Epoch: The Age of Man Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The Holocene Epoch is the current period of geologic time. The Holocene Epoch began 12,000 to 11,500 years ago at the close of the Paleolithic Ice Age and continues through today. As Earth entered a warming trend, the glaciers of the late Paleolithic retreated. Tundra gave way to forest. As the climate changed, the very large mammals that had adapted to extreme cold, like mammoth and wooly rhinoceros, became extinct. Humans, once dependent on these for much of their food, switched to smaller game and increased their gathering of plant materials to supplement their diet.  Holocene Epoch: The Age of Man Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop Evidence indicates that about 10,800 years ago, the climate underwent a sharp cold turn lasting for several years. The glaciers did not return, but game and plant materials would have been scarce. As temperatures began to rebound, human population began to increase and we began inventing the processes that would change the planet forever. Agriculture is one of the primary ways in which human activity has impacted the planet. By 8000 B.C., the cultivation of wheat, barley and other plants had spread from its origins in the Fertile Crescent through much of the Indo/European world. Domestication of sheep, goats and cattle began at about the same time.  Holocene Epoch: The Age of Man Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop Until the advent of agriculture and urbanization, the human population was largely limited by the same factors that limit other living organisms. Limiting factors in the environment, such as availability of food, water and shelter, evolutionary relationships like predator/prey ratios or presence of pathogens provide natural balances to populations. Beginning about the first century A.D., humans began to sidestep these restraints. Agriculture had increased the number of people that could be supported by the environment; we were the first animals to increase the carrying capacity of our existing habitat. Population slowly began to rise. There were approximately 170 million people on Earth at the end of the first century; by 1800, the population was over 1 billion.  Holocene Epoch: The Age of Man Many different forms of mammals and birds develop, the earth cools down after widespread heating, modern animals develop, hominids develop The Industrial Revolution of the 19th century allowed human populations to grow exponentially. Industrialization, improved sanitation and medical care caused death rates to decline, while birth rates continued to climb in most parts of the world. Science has continued to help us increase the carrying capacity of the planet, but not the size of the planet.  There have been five mass extinctions in There have been five big mass extinctions in history these are called the. Understanding the reasons and timelines of these events is important to understand the speed and scale of species extinctions today. When and why did these mass extinction events happen?  Mass extinction  There have been five mass extinctions in Evolution occurs through the balance of extinction the end of species and speciation the creation of new ones. Mass extinctions are periods with much higher extinction rates than normal. They are defined by both magnitude and rate. Magnitude is the percentage of species that are lost. Rate is how quickly this happens. These metrics are inevitably linked, but we need both to qualify as a mass extinction. In a mass extinction, at least 75% of species go extinct within a relatively (by geological standard) short period of time.3 Typically less than two million years.  There have been five mass extinctions in We see the spikes in extinction rates marked as the five events: End Ordovician (444 million years ago; mya) Late Devonian (360 mya) End Permian (250 mya) End Triassic (200 mya) many people mistake this as the event that killed off the dinosaurs. But in fact, they were killed off at the end of the Cretaceous period the fifth of the. End Cretaceous (65 mya) the event that killed off the dinosaurs.  What caused the five mass extinctions? All of the were caused by some combination of rapid and dramatic changes in climate, combined with significant changes in the composition of environments on land or the ocean (such as ocean acidification or acid rain from intense volcanic activity). Thank You For Listening  Resources Page Ritchie, H. 2022. There have been five mass extinctions in Earth’s history. Retrieved from: https://ourworldindata.org/mass-extinctions Bagley, M. 2016. Precambrian: Facts About the Beginning of Time. Retrieved from: https://www.livescience.com/43354-precambrian-time.html https://ucmp.berkeley.edu/exhibit/histgeoscale.html https://www.livescience.com/43354-precambrian-time.html https://www.jobilize.com/course/section/the-three-eras-of-the-geological-time-scale-by- openstax https://www.nationalgeographic.com/science/article/precambrian-time  Key Points The geologic time scale distinguishes Earth's history based on life-forms that existed at certain times since the planet's formation. The geologic time scale is divided into four divisions: eon, era, period, and epoch. The concept of a Geologic Time Scale is that a "period" is a basic unit of geological time during which a specific kind of rock system is produced. When "periods" are compacted together according to their characteristics, this geologic division will comprise the so-called "era." When "eras" are grouped together, this will create the longest geologic subdivision called an "eon."  Seatwork no. 2 Read/search about the history of your place or you can interview your adults about your town, on how it looks like before including the landmarks, significant landforms, historical buildings and establishment and the community folks as well. Make a narrative (at least 300 words) on how the place transforms years before up to the present. Include significant events like the physical features of the place before and now, the landmarks that were present then but it has been removed, the life forms (plants and animals) that were dominant before and now or can not be seen today. Include any information that has something to do on how your place changes over time.