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A Trip Through Geologic Time

Explore the world of fossils, from petrified remains to trace fossils, and discover how they offer clues to ancient life and Earth's transformations over time. Learn about fossil formation processes and their importance in understanding geological changes.

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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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