1. Dating Rocks!

2. Figure 7 How old is stuff? Law of superposition: Gives relative age of fossils/rock based on it’s depth.

3. The Law of Superposition Relative Age – age compared to rocks above or below. If rock layers are undisturbed, younger rocks lie above older rocks and the oldest rocks are at the bottom.

4. Index Fossils and Relative Dating Relative Age Examine fossils found in them Index fossils – you know the fossil age, so assume the rock formed during the same time the organism lived.

5. Figure 7 How old is stuff? Index fossils: Common fossils that occurred over a large area – can be used to determine the relative age of rock.

6. Figure 7 How old is stuff? Radioactive dating: Determines the absolute age of rock or fossil It is the amount of time that has passed since it was formed…looking at half-life.

7. Radioactive Dating Absolute Age – time passed since the rock formed. Common radioisotope used: potassium-40 (1/2 life of 1.3 billion years)

8. Read/Skim pages 732-734 Using complete sentences answer the following questions found on page 738: 1, 2, 6, 7, 8, 9