Fossils and Geologic Time Topics

Fossil Basics (Part 2)

•The fossil record is incomplete for many different reasons. 

• Many organisms live in environments where burial and preservation are unlikely.  Fossils are more likely to form when organisms are buried rapidly.

 • Soft-bodied animals without hard parts decay quickly. Fossils are more likely to form from hard parts such as bones, teeth, and shells.  Jellyfish and similar organisms are difficult to find fossilized.

• Weathering and erosion destroy many rocks with fossils.

• Fossils are found mainly in sedimentary rocks because these rocks form at the earth’s surface where organisms live.

Shark tooth
Shark teeth are usually the only parts of sharks that are preserved as fossils because they are the only hard parts.  Sharks belong to a group of cartilaginous fish without true bony skeletons. (Photograph by Parvinder Sethi)

This fossil is a trilobite preserved in shale.  Most fossils occur in sedimentary rocks. (Photograph by Parvinder Sethi)