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Evidence of the Past

Fossils & the Geologic Time Scale. Evidence of the Past . Fossils. Traces or imprints of any living things; physical evidence of an organism preserved by geological processes Animals, plants, bacteria, fungi Show us how life on Earth has changed

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Evidence of the Past

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  1. Fossils & the Geologic Time Scale Evidence of the Past

  2. Fossils • Traces or imprints of any living things; physical evidence of an organism preserved by geological processes • Animals, plants, bacteria, fungi • Show us how life on Earth has changed • Provide clues as to how these changes happened

  3. The Age of Fossils • Relative Dating • Oldest layers of sedimentary rocks usually on bottom • Can determine which fossils are older or younger based on position in sedimentary rock

  4. The Age of Fossils • Absolute Dating • Measures the age of fossils or rocks in years • More precise • Uses half-life of radioactive isotopes (ratio of stable to unstable atoms)

  5. Half-life Problems 100 80 60 Amount of Isotope, grams 40 Fermium-251 20 Fermium-256 0 0 2 4 6 8 10 Time, sec

  6. Half-Life Problems • 1) Nitrogen-13 has a half-life of 10 minutes. How much (what fraction) of the sample of N-13 remains after 30 minutes. • 2) If you have 40 grams of the N-13 from the problem above, how much N-13 (in grams) remains after 50 minutes.

  7. The Geologic Time Scale • The standard method used to divide Earth’s long natural history into manageable parts; calendar scientists use to outline a history of life on Earth • Eon • Era • Period • Epoch

  8. Geologic Time Scale

  9. Divisions of Geologic Time Scale • Paleozoic • “old life” • First era well represented by fossils • Mesozoic • Age of Reptiles; dominated by dinosaurs & others • Cenozoic • Age of Mammals

  10. Mass Extinctions • Periods when many species suddenly become extinct, die out completely • Rapid changes occur on Earth • Climate, volcanoes, meteorites, earthquakes, etc

  11. Changing Earth • Fossil evidence proves that continents have moved • Pangaea, “All Earth” proposed by Wegener • Wilson proposed Plate Tectonics, mechanism for Wegener’s continental drift

  12. Adaptation to Slow Changes • Rapidly changing conditions may cause extinction • Slow changes allow time for organisms to adapt • Earth conditions have changed many times throughout the history of the planet • Antarctica was once covered with tropical forests • Fossils records provide evidence of changing conditions and living organisms

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