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Geologic Time Scale

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Geologic Time Scale - Page Text Content


1: PRECAMBRIAN ERA | The Precambrian Era is divided into three periods: the Azoic, Archeozoic and the Vendian. The Azoic period was the formation of the Earth and the atmosphere and oceans. The Archeozoic is the period when first simple life forms such as bacteria and simple algae formed. The Vendian, the last period of time in the Precambrian, witnessed the rise of simple organisms such as jellyfish and sea worms. | Geologic events | -Earth forms about 4.6 billion years ago. - Oceans form and cover Earth about 4 billion years ago. -First sedimentary rocks forms about 4 billion years ago. | 4.6 billion- 544 million years ago

2: Development of Life | - Bacteria appeared about 3.5 billion years ago - soft bodied, multicellular organisms developed late in the Precambrian - First mass extinction probably occurs near the end of the Precambrian Time.

3: Paleozoic Era | The tectonic activity during the Paleozoic era is similar to the way it has always behaved but were we to see what the earth looked like at the time, the continents would look almost completely alien to the way they are now. Contrary to popular belief, the continents on earth did not begin as the supercontinent Pangaea. Before Pangaea there were older continents. At the beginning of the Paleozoic the continents were massed in another supercontinent called Pannotia. This was at the end of a global ice age. As the era progressed the supercontinent split into several smaller continents, still unrecognizable from the continents we know today. Near the end of the Paleozoic era the continents began to regroup as the supercontinent Pangaea. The collisions as the supercontinent was formed were strong enough to form mountain chains higher than the Himalayas. Among these mountain chains were the Appalachian mountains located on the east coast of North America, formed from a collision with what would become Africa. | Geologic Events | 544 billion- 245 million years ago

4: Development of Life | The beginning of the Paleozoic era is marked by a sudden explosion of invertebrate animals, over 900 recorded species in the Cambrian period. It was only a few million years later that vertebrates appeared during the Ordovician period. The Devonian period showed an uprising in fish and other marine life. By the end of the Paleozoic era evolution had caused complex land and marine animals to exist. Much of the land was dominated by large reptiles, the early ancestors of the dinosaurs. However, the event that marked the end of the Paleozoic period was the massive extinction that wiped out nearly 96% of all marine life and 70% of land animals. Only a few species survived including some reptiles. Moving into the Mesozoic era and with the competition nearly eliminated those reptiles would eventually evolve to become the lords of the earth, also known as the Dinosaurs.

5: Plant life took a little while to take off, but in the Carboniferous period the foliage thrived. The remains of the Carboniferous plant life are what form most of today's modern coal. However, this abundance in foliage declined by the Permian period and continued past the Paleozoic era into the Triassic period. At the start of the Paleozoic era the climate was moderate and shifting between stable and unstable. However, near the mid Paleozoic the climate stabilized to support all manner of land-roaming life. Near the end of the Paleozoic era the oxygen increased and carbon dioxide levels reached an all-time low causing severe ice ages in the Carboniferous period. Later, the continent Pangaea formed, creating a large surface area which caused extreme temperatures. This climate deterioration near the end of the Paleozoic may have been the cause of the mass-extinction event that marked the end of the Paleozoic era.

6: Cambrian | Geologic Events | -Shallow seas cover much of the land. -Ancient continents lie near or south of the equator. | Development of life | -Great "explosion" of invertebrates life occurs in seas. - Invertebrates with shells appear, including trilobites and mollusks. | 544-505 million years ago

7: Ordovician | Geologic Events | - Warm, shallow seas cover much of Earth -Ice cap covers what is now North Africa | Development of Life | Invertebrates dominate the oceans. - Early vertebrates-jawless fish become common. | 505- 438 million years ago

8: Silurian | Geologic Events | - Coral reefs develop. -early continents collide with what is now North America forming mountains. | Development of Life | - Fish with jaws develop -Land plants appear. - Insects ans spiders appear | 438-408 million years ago

9: Devonian | Geologic Events | -Seas rise and fall over what is now North America. | Development of Life | -Age of fishes begins as sharks and fish with scales and bony skeletons become common. - Trilobites ans corals flourish in the oceans. -Lungfish develop. -First amphibians reach land. | 408-360 million years ago

10: Carboniferous | Mississippian: 360-320 million years ago Pennsylvanian: 320-286 million years ago | Geologic Events | Development of Life | - Appalachian Mountains begin to form. - North America and Northern Europe lie in a warm, tropical region. | - Great swamp forests of huge, woody trees cover eastern North America and parts of Europe. -First rue reptiles appear -Winged insects appeared

11: Permian | 286-245 million years ago | Geologic Events | Development of Life | -Deserts become larger in tropical regions. - The super continent Pangaea forms as all continents join together. | -Reptiles become dominant on land. -Warm-blooded reptile appear. -mass extinction of many marine invertebrates, including trilobites.

12: Mesozoic Era | The Mesozoic Era is the age of the dinosaurs and lasted almost 180 million years from approximately 250 to 65 million years ago. This era includes 3 well known periods called the Triassic, Jurassic, and Cretaceous periods. A mass-extinction marked the beginning and end of the Mesozoic Era. The event that caused the transition from the Paleozoic era to the Mesozoic era was the greatest extinction this earth has seen. This extinction wiped out about 95% of all marine life and 70% of land-life. This allowed the dinosaurs to step in and settle into their role as the lords of the earth. The era ended with "The Great Extinction" which marked the end of the dinosaurs as the Cenozoic era began. | 245-66 million years ago

13: Geologic Events | At the beginning of the Mesozoic era the continents as we know them were joined together as the massive mother continent, Pangaea. It was during the age of the dinosaurs that Pangaea was transformed to the modern continents. Pangaea became two great continents known as Laurasia and Gondwana and the Atlantic Ocean began to grow. Laurasia eventually split into the continents of North America and Eurasia. Gondwana became the modern continents of South America, Africa, Australia, Antarctica, and the India subcontinent, which, after the Mesozoic era, collided with Eurasia forming the Himalayas.

14: Development of Life | The environment was unusually warm and polar ice caps did not yet exist. This played a large part in evolution and is a key factor behind the flourishing of the dinosaurs. During the Triassic period the climate was generally dry, which changed near the Jurassic period as oceans began to rise due to mounting layers of magma covering the seafloor. As a result, flooding overtook many parts of the exposed land. This allowed the climate to change with increased humidity and it continued that way even into the Cretaceous period. However, the climate began to cool during the Cretaceous although temperatures may have risen again near the end of the Mesozoic.

15: Triassic | 245-208 million years ago | Geologic Events | -Pangaea holds together for much of the Triassic. -Hot, dry conditions dominate the center on Pangaea | Development of Life | -Age of reptiles begin -First dinosaurs appear -First mammals, which evolve form warm-blooded reptiles appear -First turtles and crocodiles appear -Conifers, palmlike trees, and ginkgo trees dominate forests.

16: Jurassic | Geologic Events | Development of Life | -Pangaea breaks apart as North America separates form Africa and South America | -Largest dinosaurs thrive, including Stegosaurus, Diplodocus, and Apatosaurus - First birds appear -First flying reptiles, pterosaurus, appear. | 208-144 million years ago

17: Cretaceous | Geologic Events | Development of Life | -Continents move toward their present-day positions, as South America splits from Africa. - Widespread volcanic activity occurs. | -First flowering plants appear. -Dinosaurs including Tyrannosaurus rex, dominate. -First snakes appear. -Mass extinction at end of period causes disappearence of many land and marine life, including dinosaurs. | 144-66 million years ago

18: Cenozoic Era | The Cenozoic era, meaning "new life" is also known as the Age of Mammals, just as the Mesozoic era was the Age of Reptiles. The Cenozoic spans the time period covered from the final extinction at the end of the Cretaceous, approximately 65 million years ago, to the present. The Cenozoic era is divided into three periods, and seven systems: .During the Paleogene period the climate was tropical much like the Mesozoic. During the Neogene period, however, the earth cooled. Certain changes in the water currents formed as a result of South America joining with North America. This cooled the Arctic and, combined with other factors, created the most recent Ice Age. After time, however, the ice melted and the climate began to be much as we know it today. The three periods saw the domination of Mammals on the earth and the evolution of mankind. The Cenozoic is the age in which we live.

19: Geologic Events | During the Cenozoic era the continents moved to their modern positions. India collided with Asia in a high speed collision that caused so much geological stress that it raised the largest mountain range currently known to man, the Himalayas. Antarctica moved to the south pole, and South America slowly attached itself in a cushioned low-speed collision with North America forming the Isthmus of Panama. North America continued separating form Europe widening the Atlantic ocean. Arabia collided with Eurasia in a low-speed collision closing the Tethys ocean.

20: Tertiary | Geologic Events | Development of Life | -The Rocky Mountains and Himalayas form. -Continents continue to move into present-day position. -Continental glacier covers Antartica | -Flowering plants thrive. -First grasses appear. -Age of Mammals begins. -Modern groups such as horses, elephants, bears, rodents, and primate appear, -Ancestors of humans evolve. | 66-1.8 million years ago.

21: Geologic Events | Development of Life | Quaternary | - Thick glaciers advance and retreat over much of North America and Europe, parts of South America and Asia, and all Antartica. | -Mammals, flowering plants, and insects dominate land. -Modern humans evolve in Africa about 100,000 years ago. - Giant mammals of North America and Eurasia become extinct when the Ice Age ends about 10,00 years ago. | 1.8 million year ago to the present

23: Bibliography | Earth Science,Michael J. Padilla, Ioannis Miaoulis, Martha Cyr, Pearson Education Inc. New Jersey

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