Geologic Time Scale
Earth Science - Middle School
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Era Period Lifeforms Millions of Years Ago Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Precambrian coral sponges jellyfish trilobite ammonite brachiopod squid jawless fish shark amphibian insects jawed fish allosaurus compsognathus brachiosaurus pterosaurus saber-tooth tiger rodent eohippus coryphodon wooly mammoth archaeopteryx The geologic time scale is a map that divides Earth’s history into logical segments of time. The oldest portion is at the bottom of the scale and the youngest is at the top of the scale. The divisions on the scale mark significant transitions in Earth’s history. Most often, these transitions represent important, and sometimes dramatic, changes in the life forms present on Earth and significant changes in geologic history. The geologic time scale is broken into divisions and subdivisions. The broadest divisions are called eons. Eons are divided into eras, eras are divided into periods and periods are divided into epochs. The Paleozoic Era The Paleozoic Era literally means “old life.” It lasted from 540 million years ago to 248 million years ago. At the beginning of the Paleozoic (the Cambrian Period), there were only simple life forms. By the end of the Paleozoic, amphibians crawled out of the water to venture onto land and insects were abundant. The middle of the Paleozoic marked the growth of land plants and trees. Of all the Eras, the Paleozoic Era contains the most extensive collection of fossils. The Paleozoic fossil record includes simple organisms such as algae, through marine invertebrates like brachiopods and corals, to early amphibians. This era ended with a mass extinction of over 90 percent of all species. This is known as the Permo-Triassic Extinction. The Mesozoic Era The Mesozoic Era literally means “middle life.” It lasted from 248 million years ago to 65 million years ago. This is the era that is most popularly known as “The age of the Reptiles.” Some even call it “The age of the Dinosaur.” It is during this era that life crawled out of the water and learned to live exclusively on land. Even though the reptiles were the most dominant of animals, early birds and small mammals also began to appear on the landscape. The end of the Mesozoic Era is marked by another mass extinction. It is estimated that about 50% of all species, including all of the dinosaurs, became extinct at the end of the Mesozoic Era. The Cenozoic Era The Cenozoic Era literally means “recent life.” It began 65 million years ago and continues to the present day. This era is most commonly referred to as the “Age of the Mammals.” The demise of the dinosaurs at the end of the Mesozoic Era allowed the growth and ultimately the dominance of mammals. The Cenozoic Era has also been marked by dramatic climatic changes that have allowed periods of glaciation followed by periods of melting and glacial retreat. 544 to 4.6 million years ago 144 208 286 360 408 438 505 544 66.4 245 1.8 to present © Copyright NewPath Learning. All Rights Reserved. 94-4104 www.newpathlearning.com Geologic Time Scale
Era Lifeforms Period Millions of Years Ago 1.8 to present 544 to 4.6 million years ago Precambrian \|xiBAHBDy01789pzY What is a geologic time scale? __________________________________________________________________________________ The geologic time scale is broken into _________________________ and _________________________ . The broadest divisions are called _________________________ . Eons are divided into _________________________ , eras are divided into _________________________ and periods are divided into _________________________. The Paleozoic Era Describe: ___________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ The Mesozoic Era Describe: ___________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ The Cenozoic Era Describe: ___________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ ____________________________________ Key Vocabulary Terms • Cambrian Period • Carboniferous Period • Cenzoic Era • Cretaceous Period • Devonian Period • division • eon • epoch • era • geologic time scale • Jurassic Period • Mesozoic Era • Ordovician Period • Paleozoic Era • period • Permian Period • Quaternary Period • Silurian Period • subdivision • Tertiary Period • Triassic Period © Copyright NewPath Learning. All Rights Reserved. 94-4104 www.newpathlearning.com Geologic Time Scale
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