Fossils provide evidence of past life by preserving the remains or traces of prehistoric organisms. Certain fossils called index fossils are associated with a particular span of geologic time, allowing scientists to date rock layers based on the fossil types present. The principle of fossil succession states that different fossils are found in different rock layers based on the period of time when those organisms were alive.

1. 12.2 Fossils: Evidence of Past Life

2. Fossil
• The remains or traces of an organism
preserved from the geologic past

3. Index fossil
• A fossil that is associated with a particular
span of geologic

4. Key Concept
• Fossils are the remains or traces of prehistoric
life. They are important components of
sediment and sedimentary rocks.

5. Key Concept
• The type of fossil that is formed is determined
by the conditions under which an organism
died and how it was buried.

6. Key Concept
• The principle of fossil succession states that
fossil organisms succeed one another in a
definite and determinable order. Therefore,
any time period can be recognized by its fossil
content.

7. Key Concept
• Index fossils are widespread demographically,
are limited to a short span of geologic time,
and occur in large numbers.

8. Key Concept
• Fossils can also be used to interpret and
describe ancient environments.