Chapter 13:1 Fossils

A. Paleontologists – scientists who study fossils and reconstruct the appearance of animals

B. Fossils – remains, imprints, or traces of prehistoric organisms

1. Fossils can form if the organism is quickly buried by sediment.

2. Organisms with hard parts are more likely to become fossils than organism with soft parts.

3. You can see pictures of fossils at http://www.fossilmuseum.net/FossilGalleries.htm

C. Types of preservation. (preservation means to keep in existence, or to make lasting)

1. Permineralized remains - Fossils in which spaces inside are filled with minerals from ground water.

2. Carbon film – results when a thin film or carbon residue forms a silhouette of the original organism. (carbonized plant materials become coal).

Carbon films

3. Mold – a cavity (space) in rock left when the hard parts of an organism decay.

4. Cast – produced when sediments fill in a cavity made when an object decayed.

Casts and Molds

http://esp.cr.usgs.gov/info/kt/footprint.htmlhttp://petrifiedwoodmuseum.org/MoldsCasts.htm

Mold

Mold

Mold

Cast

Cast

Cast

5. Original remains – occasionally the soft parts of an organism are preserved in ice, tar, or amber.

6. Trace fossils – provide evidence of an organism’s activitiesa. Can be footprints left in

mud or sand that became stone.

b. Can be trails or burrows made by worms and other animals.

Gyrolites – a burrow made By an ancient arthropod

D. Index fossils – abundant, geographically wide spread organisms that existed for relatively short periods of time.

E. Fossils can reveal information about past land forms and climate.

1. Fossils of marine organisms have been found in areas that are currently deserts.

2. Tropical plant fossils have been found in regions that are now temperate.

Click to see how a fossil forms

We’ve talked about relative ageF. How old something is in

comparison with something else is its relative age

• Superposition tells us that older rock layers are on the bottom and younger rock layers are closer to the top.

I’m the youngest!

I’m the oldest

G. Absolute age— is the age, in years, of a rock or other object; determined by properties of atoms

How old are you?

It’s my birthday!

46 million years! Happy

Birthday!