Fossils and Time

1. Fossils and Time

2. What’s a Fossil? • Defined as any remains, trace, or imprint of an animal or plant that has been preserved in Earth’s crust during prehistoric times. • Not all fossils are the remains of once-living organisms; some are just traces left behind like burrows, tracks, and droppings (poop).

3. How do fossils form? • Conditions must be ‘just right’ • When a plant or animal dies, the remains must be buried quickly before decomposition takes place. • The hard parts such as shells, bones, and teeth are usually the remains most often found as fossils. • It can take millions of years for sediments to turn into rock

4. Vocab • A mold of a shell may be left if the shell dissolves over time. • Sometimes, minerals may fill the mold forming a cast that duplicates the original shell. • That process is called replacement. • Petrifaction is a process that occurs in wood. When water with lots of minerals in it fills the pores of trees it turns it into rock. • Carbonization occurs when sediments flatten a plant and turn it into a thin, carbon film.

5. How does carbonization form coal? • Write a 1-2 sentence summary on the process. • http://www.ket.org/trips/coal/agsmm/agsmmhow.html

6. Some amazing fossil exceptions... • The Burgess Shale in British Columbia is famous for its soft-bodied fossils. • http://science.discovery.com/videos/100-greatest-discoveries-shorts-burgess-shale-creation.html

7. What are the major fossil groups? • Corals: horn-shaped sea creatures • Bivalves: shellfish like clams or mussels • Brachiopods: type of shellfish now nearly extinct with symmetrical shells • Gastropods: snail-like animals • Cephalopods: free-swimming squid-like creatures with shells • Trilobites: extinct sea creatures similar to the horseshoe crab • Crinoids: known as sea lilies • Plant fossils: widespread, but sparse. Mostly ferns

8. The Law of Fossil Succession • The kinds of animals and plants found as fossils change over time. • They succeed after one another in a definite recognizable order • This is how we know the relative age of rock layers. • If we find the same kind of fossils in rocks from different places, we can infer the rocks are the same age.

9. Index Fossils • Organisms that had short lives, but are excellent time markers pinpointing the age of rock layers • The best index fossils are the ones with a wide geographic existence, are abundant, and easily identifiable.