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A Trip Through Geologic Time

A Trip Through Geologic Time. Division 2 MST. Evidence of Ancient Life . Fossils Preserved remains or traces of living things. Provide evidence of how life has changed through time. Help scientists infer how Earth’s surface has changed.

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A Trip Through Geologic Time

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  1. A Trip Through Geologic Time Division 2 MST

  2. Evidence of Ancient Life • Fossils • Preserved remains or traces of living things. • Provide evidence of how life has changed through time. • Help scientists infer how Earth’s surface has changed. • They are clues to what the environments of the past were like.

  3. How do fossils form? • Most form in areas where sediments build up. • Near swamps, lakes or shallow seas • Only the hard parts of the animals are left after the soft tissues decay or are eaten. • The remains must then be protected from decay

  4. How do fossils form? http://www.youtube.com/watch?v=SEDfRy6DQns&feature=related

  5. Kinds of Fossils • Petrified fossils • Form when the remains of an organism become petrified (in other words "turned to stone”) • Minerals replace all or part of an organism

  6. Petrified Ammonite

  7. Petrified Wood

  8. Petrified Wood

  9. Kinds of Fossils • Molds and Casts • Most common • Copy shape of organism • Mold is a hollow area in sediment in the shape of the organism • Forms when hard parts buried in sediment • Cast is a copy of the shape of the organism due to dissolved minerals and sediment deposited in the empty space of a mold. • Molds and Casts are Opposites!

  10. Which is which? Cast or Mold?

  11. Kinds of Fossils • Carbon Films • An extremely thin coating of carbon on rock • When sediment buries an organism, the weight of the sediment squeezes almost all of the decaying organism away, until only a thin film of carbon remains.

  12. Carbon Film FossilRedwood Tree leaf

  13. Kinds of Fossils • Trace Fossils • Provide evidence of activity • Example: a footprint, burrow trails • Trace fossils provide geologists with much useful information about ancient water depths, paleocurrents, availability of food, and sediment deposition rates

  14. Trace Fossils

  15. Kinds of Fossils • Preserved Remains • Some processes preserve the remains of organisms with little or no change. • Example: Trapped in Tar, amber or freezing

  16. Insect in Amber

  17. Kinds of Fossils • Index Fossils • A fossil preserved in a rock layer that is characteristic of a certain span of geologic time or environment. • Must represent an organism that existed only briefly • They tell the relative ages of rock layers in which they occur

  18. Index FossilTrilobite

  19. More Examples...

  20. Review Time! • Answer the following questions IN COMPLETE SENTENCES and in your own words, on the sheet at your table to be passed in at the END of class: • Describe the process which most fossils are formed in rock. • How does the fossil record support the theory of evolution?

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