1. Earth’s History is Recorded in Rocks Two Methods to Date Rocks.

2. Relative Age  How old your relatives are.  Age of an object compared with the ages of other objects. –The blackboard is older than the chalk on it.  How do you determine relative age? –Relative Dating  Dating in the South.

3. Absolute Age  Actual age of an object.

4. Methods of Estimating Absolute Age 1. Rates of Deposition 2. Rates of Erosion 3. Using Chemistry

5. Radioactive Decay  Atoms that are unstable (too much energy) decay (lose energy) at a constant rate into other, more stable, substances.

6. Radioactive Decay Continued  Lose protons to become more stable.  Happens in the nucleus.  Unstable elements (parent isotope) change into more stable isotope (daughter isotope). –Isotope – Elements with the same number of protons, but a different number of neutrons.  Example – C-12 & C-14 (2 more neutrons)

7. Half Life  The time required for half the mass of a radioactive element to decay into its daughter elements.  Decay rate is always constant.

8. Carbon Dating  Carbon Dating –Uses the isotope C-14 (parent element). –Living things ingest C-14 in the CO 2 in the atmosphere. Whey they die they don’t and it decays to form the daughter element N-14. –½ life of C-14 is 5,730 years. –Only used for organic materials. –Only good up to about 50,000 years.