III. THE FOSSIL RECORD
- fossils – the trace or remains of an organism that lived long ago,
most commonly preserved in sedimentary rock
- fossils are an important source of information for finding the
relative and absolute age of rocks
- provide clues to the past
- geological events
- climate
- evolution of living things
- paleontology – the scientific study of fossils
- almost all fossils are discovered in sedimentary rock
A. Interpreting the Fossil Record
1. provide important clues to the environmental changes that
occurred in Earth’s past
2. scientists use this information to learn about how environmental
changes have affected living organisms
B. Fossilization
1. only dead organisms that are buried quickly or protected from
decay can become fossils
2. generally, only the hard parts of organisms become fossils
a. wood
b. bone
c. shells
d. teeth
3. in some instances, only a replica of the original organism
remains (Table 1 page 198)
C. Trace Fossils
1. fossilized evidence of past animal movement
2. examples
a. tracks
b. footprints
c. borings
d. burrows
3. an important clue to the animal’s appearance and activities
D. Index Fossils
1. a fossil that is used to establish the age of rock layers
2. four requirements
a. present in rocks scattered over a large region
b. features that clearly distinguish it from other fossils
c. organisms must have lived for a short period of time
d. fossils must occur in fairly large numbers within the
rock layers
E. Index Fossils and Absolute Age
1. index fossils are used to determine absolute age
2. rock layers containing index fossils can be dated accurately
3. index fossils can be used to date rock layers in separate areas