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Geologic Time Scale

Geologic Time Scale. Geologic Time Scale. A record of the life forms and geologic events in Earth’s history . Scientists developed the geologic time scale by studying rock layers and index fossils worldwide.

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Geologic Time Scale

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  1. Geologic Time Scale

  2. Geologic Time Scale • A record of the life forms and geologic events in Earth’s history. • Scientists developed the geologic time scale by studying rock layers and index fossils worldwide. • Index fossils - a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found. • For example, if you find a fossil from an unknown era near a fossil from a known time, you can assume that the two species were from about the same time. • Scientists placed Earth’s rocks in order by relative age. • Later, radioactive dating helped determine the absolute ageof the divisions in geologic time scale.

  3. Let’s Review: Relative Age vs. Absolute Age

  4. Divisions of Geologic Time • As scientists studied the fossil record, they found major changes in life forms at certain times. • They used these changes to mark where one unit of geologic time ends and the next begins. • Divisions of the geologic time scale depend on events in the history of life on Earth.

  5. Geologic time begins with a long span of time called Precambrian Time. Covers 88% of earth’s history. It ended 544 million years ago. • Time between Precambrian and now is divided into 3 eras—Paleozoic, Mesozoic and Cenozoic. • Eras are subdivided intoperiods. Names of periods come from places around the world where geologists first described the rocks and fossils of that period. • Periods are divided into Epochs.Epochs are the shortest division of time.

  6. Pangaea the “Super-continent” Pangaea – “all lands” • Alfred Wegener hypothesized that the continents had moved! (early 1900’s) • They were once joined together in a single landmass. (300 MYA) • Over tens of millions of years Pangaea began breaking apart and eventually towards were the sit today. • This idea became known as Continental Drift.

  7. Evidences of Pangaea • Landforms • Fit together like puzzle pieces • Mountain ranges from Africa and South America line up. • Fossils • Fossils from the same fern like plant found in Africa, South America, Australia, India, and Antarctica. • Climate • Fossils of tropical plants found in the Arctic • According to Wegener, Earth’s climate has not changed, the positions of the continents have!

  8. Evidence worksheet • Top portion as a group • Answer questions on bottom for homework.

  9. Evidences for Pangaea Map Eurasia North America South America Africa India Australia Antarctica

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