Absolute Dating

1. Absolute Dating Radioactive Dating

2. Radioactivity • Almost all of the elements contain radioactive isotopes • Isotopes are atoms of the same element with different atomic weights • This is due to different numbers of neutrons in the nucleus.

4. Radioactivity • The rate at which radioactive elements break down is predictable and specific to different isotopes. • The rate of decay is not affected by external factors such as temperature, heat or pressure

5. Radioactivity • We measure time of decay in Half-Life • A Half-Life is the time it takes for the mass of one half of the radioactive element to decay into its daughter product.

7. A graph of radioactive decay looks like this:

8. Absolute Dating • By comparing the ratio of Parent product to daughter product you can calculate the number of half-lives that have passed • Materials with long half-lives are used to date old materials • Materials with short half-lives are used to date young materials

10. Absolute Dating • The age of the Earth was determined by the breakdown of different isotopes of uranium.

12. Absolute Dating • Carbon 14 (C14) is often used to date materials that were once alive. • While the organism is living the amount of C14 remains constant because of the exchange of carbon

13. Absolute Dating • When the organism dies the C14 breaks down into N 14 • Due to the relatively short half-life of 5700 years C14 is not useful for dating very old objects