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Transcript
The Tertiary Period Overview: The Tertiary Period began 65 million years ago and lasted more than 63 million years, until 1.8 million years ago. During the Tertiary Period there were many changes in climate and in the types of species around the world. One of the most important facts about this period is that with nearly all of the dinosaurs gone, there was plenty of room on Earth for the mammals and birds to have lots of babies, and soon there were all different kinds of mammals and birds all over the Earth. The Tertiary Period ended with the planet’s last great Ice Age. Earth Environments: Plate tectonics were very active during the Tertiary Period. Some continents ran into each other: about 60 million years ago California ran into North America, causing the Rocky Mountains. About 55 million years ago India crashed into Asia and made the Himalaya mountains, and about 30 million years ago Africa crashed into Europe and pushed the Alps up into mountains. All of this movement began to arrange the continents into the way we see them now. The beginning of the Tertiary Period was very warm and moist compared to today’s climate. Much of the earth was tropical or sub-tropical. Palm trees grew as far north as Greenland! As plate tectonics made the continents drift apart, it caused a lot of volcanoes. The carbon dioxide released by these volcanoes cooled down the Earth gradually throughout the Tertiary period. This cooling trend continued and by the end of the Tertiary Period, an ice age had begun. The mountains of the world were covered by glaciers (including the newly formed Himalayas and Alps). The huge amounts of water locked up in the ice lowered the level of the sea and land bridges appeared. This enabled migrations of both plants and animals across these land bridges. The Tertiary period, which had begun hot and humid, ended in a cold dry ice age. Life Forms: The extinction event at the close of the Cretaceous Period wiped out the dinosaurs, large reptiles, and many other species. This left room for new animals to take over. The mammals became the dominant animals. Most of the main groups of mammals were present during the Tertiary Period. With the dinosaurs and other large reptiles gone mammals grew in size, numbers and diversity. They found homes and made a living in the sea, on land, and in the air. Birds did almost as well as mammals during the Tertiary Period. Many of the birds we know today were present. There were also many large flightless birds that are now extinct. These birds did particularly well before the mammals developed so many species. Probably the most important thing to occur during the Tertiary period happened around six million years ago. Fossil evidence shows that at that time the first people evolved out of the early primates in Africa. By 2.5 million years ago, these people were using stone tools and entering what we call the Paleolithic period of human history. The Precambrian Era Overview: The Precambrian is the name which describes the large span of time in Earth's history. It spans from the formation of Earth around 4600 million years ago to about 542 million years ago. The Precambrian accounts for 88% of geologic time. Very little is known about the Precambrian, despite it making up a large part of the Earth's history. The Precambrian fossil record is poor. This is because many Precambrian rocks have undergone heavy pressure and temperature turning them into metamorphic rocks. This process makes it difficult to determine where they came from. Many of the rocks from the Precambrian era have either been destroyed by erosion, or remain deeply buried in the earth’s crust. Earth Environments: Details of tectonic plate motions are not well known in the Precambrian. It is generally believed that small continents existed prior to 3000 Ma, and that most of the Earth's landmasses collected into a single supercontinent around 1000 Ma. The supercontinent, known as Rodinia, broke up around 600 Ma. A number of ice ages have been identified going as far back as 2200 Ma, in which the entire globe was covered in snow and ice. The Earth might have looked something like the image below, in which there were cold conditions all the way to the equator, resulting in something scientists call "Snowball Earth". The atmosphere of the early Earth is poorly known, but it is thought to have very little oxygen. When evolving life forms developed photosynthesis, oxygen began to be produced in large quantities, causing an ecological crisis sometimes called the oxygen catastrophe. The oxygen was immediately tied up in chemical reactions, primarily with iron. Scientists know this because older rocks contain massive banded iron formations that were apparently laid down as iron and oxygen first combined. Life Forms: It is not known when life originated. Well-preserved bacteria older than 3.46 billion years have been found in Western Australia. Possible fossils 100 million years older have been found in the same area. A diverse collection of soft-bodied forms (like jellyfish) were found from a variety of locations worldwide between 542 and 600 Ma. Hard-shelled creatures appeared toward the end of that timespan. The oldest fossil evidence of complex life is found at least 580 million years ago. The Permian Period Overview: The Permian Period is the final period of the Paleozoic Era. It began about 290 million years ago and lasted until 248 million years ago. The greatest mass extinction that has ever occurred on earth took place at the end of this 42-million- year period. There are many theories about the cause of the Permian extinction, but many scientists hypothesize it could ha ve been caused by huge amounts of volcanic activity. We know from recent volcano eruptions that large eruptions can cause the temperature to drop all around the world. The Permian Period gets its name from a region of west-central Russia called Perm Oblast. This is where rocks from this time were first found. Even though it was first found in Russia, this layer of rock can be found across the world. Earth Environments: For most of the Permian, life on Earth was much like it had been in the Carboniferous. Temperatures were cooler because the continent of Pangea was moving northward. Mountains were forming as the supercontinent Pangea moved. When the continent of Siberia collided into the northern part of Euramerica, Pangea was complete. The Ural Mountains were pushed up by this collision. Pangea was shaped like a large “C.” It surrounded the Tethys Sea. The rest of the Earth was covered by a huge ocean named Panthalassa. Even though the ocean covered much of the earth, Pangea was so large that the interior did not benefit from the ocean waters. Deserts were places in the center of Pangea where the temperatures changed from very cold to very hot. In some places there was rarely or never any rain. Over all the earth was dry during the Permian Period. Life Forms: The dry climate was bad for water-loving plants and animals like ferns and frogs, but good for dry land plants and animals, so there got to be a lot more of them. The first reptiles were already living on land, but during the Permian period there got to be many more reptiles, and more different kinds of reptiles. Pelycosaurs evolved from their beginnings in the Carboniferous. These animals look like a reptile, but have skull characteristics that are similar to mammals. The most famous of the pelycosaurs is the Dimetrodo n. Like many other pelycosaurs, fossils show that Dimetrodon had a large sail on its back. The sail could have been used to help keep the body temperature stable in the dry Permian environment. New plants developed that were adapted to the dryer conditions. These plants had seeds. One of the earliest of these plants still exists today. It is called the Ginkgo. Most of the trees living during the Permian period were conifers. Conifers are trees with seeds in cones, like Pine Trees. Just like with animals paleontologists find fossils of these types of trees in layers of rock from the Permian Period. During the Permian Period, these plants and animals spread across the land. It was easy for these trees and reptiles to spread all over because the land was all joined together in one big continent. Similar fossils from this period can be found all across the continents today. The Cretaceous Period Overview: The Cretaceous Period covered the time span of 144 million years ago to 65 million years ago. There was a minor mass extinction at the end of the Jurassic Period that is the sign of the beginning of the Cretaceous. Many of the species of bivalved mollusks (similar to clams) became extinct at this time. There seems to have been a serious event that caused the major mass extinction at the end of the Cretaceous Period. It is called the KT event for (K)Cretaceous and (T) Tertiary, the first period of the Cenozoic Era which follows. A popular theory is that a meteor hit the earth in the Gulf of Mexico. This caused many geologic activities. Volcanoes erupted, clouds, smoke, and dust covered the skies keeping the sun’s light away from the planet for years. This would have caused huge changes in the climate and vegetation, and it is likely responsible for the extinction of the dinosaurs as well as many other types of life. Earth Environments: During the Cretaceous Period continents drifted away from each other, as the continents separated, the climate got cooler and rainier, and there was even snow in some places and glaciers on high mountains. But by the middle of the Cretaceous period, the movements of the tectonic plates caused a lot of huge volcanic eruptions all over the planet, and these volcanoes shot large amounts of carbon dioxide into the air. The greenhouse effect of all this carbon dioxide caused a global climate change that warmed up the planet again. Many of these volcanic eruptions happened underwater in th e area that is now our Atlantic Ocean. These volcanoes created underwater mountains that grew as the Atlantic Ocean got wider. As these mountains grew they moved so much water that the oceans were about 100 meters higher than today! This caused many inland seas to form. In North America, an inland sea divided the continent across the plains of modern-day Canada, imagine a sea going through the middle of North America! Life Forms: The fossil record shows that animal life continued to develop during the Cretaceous Period and new species of dinosaurs became important. The ceratopsian dinosaurs appeared for the first time. These were plant-eating dinosaurs and the most famous example is the triceratops. It had three horns and a huge, bony frill that formed its skull. But probably the most famous dinosaur of all lived during the Cretaceous Period, and it wasn’t a plant eater! The Tyrannosaurus ruled the land at the end of the Cretaceous Period. Tyrannosaurus was a large theropod dinosaur. Like all theropods it walked on two legs and was carnivorous. Although not as successful as the dinosaurs fossils show small mammals existed during the Cretaceous Period, but they were not very important. These were tiny creatures compared with the giant dinosaurs. Unlike the dinosaurs that laid eggs, these mammals developed their offspring inside their bodies. Birds were another important type of animal to develop and become more common at this time. Mammals and birds would become very important after the KT extinction event wiped out the dinosaurs at the end of the Cretaceous Period. Probably the most important development for life had nothing to do with animals though! The most important development of the Cretaceous Period was the growth of flowering plants. Before this, most of the trees had been plants with cones. Now trees began to produce flowers. The ancestors of many modern tree species appeared during the Cretaceous including the magnolia and the maple. The Carboniferous Period Overview: About 359 million years ago, the Carboniferous period got started and lasted until about 290 million years ago. It lasted for about 64 million years. The name “Carboniferous” came from the large amounts of carbon-bearing coal that was formed during the period. Environmental Conditions: When these ferns died, they formed thick layers of dead plants that eventually turned into coal. Most of the coal in the world today comes from ferns that grew during the Carboniferous period. So much carbon got used up making coal that there wasn't enough to combine with oxygen to make carbon dioxide, and instead the oxygen atoms had to just make oxygen molecules. Because of that, oxygen levels in the atmosphere rose much higher than before (and higher than they are now). Plate tectonics caused the Euramerica continent to smash into Godwanaland, pushing the land up to make the Appalachian Mountains that run along the Atlantic coast of North America. Asia also ran into the other side of Europe to make the Ural Mountains. These are some of the oldest mountains that are still around today. These mountains had no plants covering them. During rainy seasons huge amounts of surface rock was washed into flood plains and deltas. The end of the Carboniferous period is marked by global climate changes due to the glaciers that covered the South Pole. The mass extinctions that mark the end of other geologic periods were not present, yet many species did go extinct during this time. The marine environments were most affected by these climate changes, so the extinctions were mostly invertebrates that spent their lives in the seas. Life Forms: Although insects like spiders had already land for many millions of years, now some of fly like flies or dragonflies. Animals with were just beginning to get started on land. animals, amphibians like frogs, had to go ocean to lay their eggs. The frogs evolved to because that was the only kind of land animal this time. been living on them began to backbones These earliest back to the eat insects, there was at But by about 310 million years ago, the climate was changing. It was getting much drier and hotter on land. So the plants and animals evolved to take advantage of that. Some early pine trees developed the ability to make seeds, so they could make baby pine trees even where there wasn't any water for their spores. And, in the same way, some of the amphibians developed into reptiles with the ability to lay eggs with hard calcium shells, so they could lay eggs on land in dry places and didn't need to stay near the water anymore. Insects also grew well in the humid and high-oxygen conditions. One of the largest was the Meganeura. This large ancestor of the dragonfly had a wingspan of 60 to 75 cm. Another large arthropod lived on the floor of the Carboniferous forests. The Arthropleura was a giant millipede that could grow to more than one and a half meters long. They sometimes had as many as 30 pairs of legs! The Cambrian Period: An Explosion of Life Overview: The Cambrian Period marks the beginning of the Paleozoic Era. It immediately follows the Precambrian Era. The period lasted for nearly 53 million years, from about 543 million years ago until 490 million years ago. The Cambrian Period began with an explosion of life forms. It ended in a mass extinction. Environmental Conditions: The climate at the beginning of this period was cold, but over time the climate in all parts of the Earth grew warmer. There were no glaciers at the North or South Pole. This made the seas a good place for many species to live. The continents were still forming. They were mostly barren rocks. The land had no plant or animal life on it yet. Earth's land was broken up into smaller continents, but they were drifting closer together, and about 500 million years ago plate tectonics brought all of the land on Earth together to make a new supercontinent called Pannotia. Towards the end of the period, advancing glaciers would have lowered the temperature of the shallow seas where so many species lived. Changes in the temperature and the amount of oxygen in the water would have meant the end for any species that could not adapt. Life Forms: During the Cambrian Period there was an explosion of life forms. Most of these were in the water. Many animals with no backbones lived in the shallow seas. These animals were invertebrates. One species was so plentiful and had such numbers and so many species that it is called the ruling species of the period. This called a trilobite. The trilobite was an with a tough outer skin. It got its name from lobes in the hard skin. The trilobite was also first animals to have eyesight. During the there were more than 100 types of trilobites. great sometimes species is arthropod the three one of the Cambrian There were plenty of other species living during the Cambrian Period also. Mollusks, worms, sponges and echinoderms filled the Cambrian seas. Sponges grew in Cambrian seas, too. There was even an early type of early fish living during the Cambrian Period. It was the Pikaia. Pikaia looked a bit like a worm with a long fin on each side of its body. The nerve cord was visible as a ridge starting behind the head area and extending almost to the tip of the body. One of the most fearsome hunters in the seas was the Anomalocaris. This animal exoskeleton like an arthropod, but it did not jointed legs that would make it a true This large animal fed on trilobites and other worms and mollusks. Cambrian had an have the arthropod. arthropods, Many of the creatures living in the Cambrian seas developed hard structures for defense, hard shells, scales, and spikes covering the outside of the body. The plants of the Cambrian were mostly simple, one-celled algae. The single cells often grew together to form large colonies. The colonies looked like one large plant.