Section 18.1,18.2 By: Christian Flores and Jordan GEOLOGICAL TIME SCALE Section 18.1,18.2 By: Christian Flores and Jordan

Section Objections Summarize the development of the geologic column. List the major units of geologic time. identify the characteristics of Precambrian rock Explain what scientists have learned from the geological record about life during the Paleozoic era. Explain what scientist have learned from the geologic record about life during the Cenozoic era.

New Vocabulary Cenozoic Era- The most recent geologic era, beginning 65 million years ago; the Age of Mammals. Epoch- Subdivision of a geologic period. Era- Largest unit of geologic time. Geologic Column- Arrangement of rock layers based on the ages of the rocks. Invertebrate- An animal without a backbone Mesozoic Era- Geologic era that lasted from 245 million years ago; the Age of Reptiles. Paleozoic Era- Geologic era that followed Precambrian time, lasting from 570 million to 245 million years ago. Period- Subdivision of a geologic era. Precambrian Time- earliest and longest geologic era lasting from 4.6 billion to 570 million years ago. Theory Of Evolution- Theory that organisms are derived from ancestral types. Vertebrate- An animal with a back bone.

The Geologic Column Using the law of superposition and the study of index fossils, nineteenth-century scientists determined the relative ages of rock layers in the areas throughout the world. No single area on the earth contained a record of all geologic time. Scientist combined their observations from around the world to create a standard arrangement of rock layers called now the geologic column. Rock layers in the geologic column are distinguished by the fossils they contain and the rock type.

Divisions of Geologic Time Is divided into units. Geologist use events like earth’s geologic history, major changes in the earth’s surface or climate changes to dived them into units. A unit is often characterized by fossils of a dominant life-form.

Eras A very large unit of geologic time is an era. Earliest is Precambrian Era. It is known more as Precambrian time because it is much longer then other geologic eras. When this era started earth’s crust was just beginning to solidify. It lasted for 4.6 billion years Paleozoic Era followed Precambrian time. It means “ancient life”. It lasted 325 million years. They contain fossils of marine and land plants and animals. Mesozoic Era followed the Paleozoic Era. It “means middle life”. These fossil's contain more complex forms. It lasted 180 million years. The Cenozoic Era followed the Mesozoic Era. It means recent life. The fossils of mammals are common in this era. This era started 65 million years ago and still continues today.

Periods and Epochs Eras have been divided into shorter times called periods. Each period is characterized by specific fossils and usually named for the location in which the rocks containing the identifying fossils. Epochs are even shorter time periods then periods.

Precambrian Time Began nearly 4.6 billion years ago and ended 570 million years ago. It makes nearly 88% of earth’s history. Large areas of exposed rock Precambrian rocks, called shields are found in every continent, one of these shields covers much of eastern Canada. Fossils are rare in Precambrian rocks because the life forms used to have soft bodied. These organisms lacked bones, shells and other hard parts needed to make a fossils.

The Paleozoic era Began 570 million years ago ended 245 millions years ago Had Cambrian period, Ordovician period, Silurian Period, Devonian Period, Carboniferous Period, Permian Period.

The Mesozoic Era Began 245 million years ago ended 65 million years ago. Had Triassic Period, Jurassic Period, and Cretaceous Period.

The Cenozoic Era Began 65 million years ago and it still continues today. Had Quaternary Period, and Tertiary Period. Also had these epochs Holocene, Pleistocene, Pliocene, Miocene, Oligocene, Eocene, Paleocene.

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