Looking at Fossils 12/16/146-4 pgs. 146-150

IN: How do you think fossils form?

Put your DRW on the box

What are fossils?

Fossil – any naturally preserved evidence of life.

Types of Fossils1. In Rocks2. Petrification3. In Amber4. Mummification5. Frozen Fossils6. In Tar7. Trace Fossils8. Molds and Casts

1. In RocksOccasionally, body parts get

buried quickly in sediment and are preserved while the sediment turns to rock.

What type of rock has fossils?Sedimentary

Mineral Replacement

2. Petrification – a process in which an organism’s tissues are completely replaced by minerals.

3. In AmberHardened tree sap is called

amber.

4. MummificationWhen organisms die in dry

places, such as deserts, they can sometimes dry out so fast that there isn’t enough time for even their soft parts to decay.

5. Frozen FossilsAnimals freeze in glaciers and

are preserved until the glacier thaws thousands of years later.

6. In TarOrganisms get trapped and sink

in tar pits which preserve the organism.

La Brea Tar Pits, Los Angeles

7. Trace Fossils – any naturally preserved evidence of an animal’s activity.

Tracks

Johnson Farm – St. George, Utah

Coprolites – preserved feces.

8. Molds and CastsA mold is a cavity in the ground

or rock where a plant or animal was buried.

A cast is an object created when sediment fills a mold and becomes a rock.

Using Fossils to Interpret the PastFossils can reveal changes that have occurred in parts of the Earth.◦Coral-reef fossils have been found in Iowa.

◦Fossils of marine organisms have been found on tops of mountains in Canada.

Using Fossils to Date Rocks

Index fossils – a fossil that is used to date the rock layers in which it is found.

Tropites lived between 230 million and 208 million years ago.

OUT: If you find rock layers containing fish fossils in a desert, what can you infer about that area of the desert?