1. The Position of Rock Layers
- The Relative Age of Rocks
The Position of Rock Layers
1) According to the Law Of Superposition, in horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it. The law of superposition states that each undisturbed rock layer is older than the rock above it.

2. Relative Age
2) Relative Age explains that something is “older” or “younger” than another object, but absolute (actual) age is unknown. The age of an object compared to the age of another object is relative age.

3. 3) How a Fossil Forms:
- Fossils
Most fossils form when living things die and are buried by sediment. The sediment slowly hardens into rock and preserves the shapes of the organisms.

4. How can fossils help us determine the age of rocks?
INDEX FOSSILS!!

5. 4) Using Fossils to Date Rocks:
- The Relative Age of Rocks
4) Using Fossils to Date Rocks:
Index fossils are useful because they tell the general ages of the rock layers in which they occur.

6. To be an index fossil the fossil had to have been:
Alive for a relatively short period of time, then it went extinct.
When it was alive, it was widespread over the earth.

8. Fossils and geological time– THE BIG IDEA!!
5) Rock layers are correlated (formed at about the same time in history) if they both contain the same index fossils.
The age of an object compared to the age of another object is relative age.
The law of superposition states that each undisturbed rock layer is older than the rock above it.

9. Your assignment…
Draw a rock bed with three layers (yellow, red and green). Color the oldest layer green. Color the youngest layer red. Draw fossils that show fish only lived during the middle age and birds lived in both the youngest and oldest layer.