Absolute Age

1. Absolute Age Actual Age

2. Radioactive Decay • Nuclei of unstable atoms break down or decay, giving off particles and energy • Process continues until the atoms are stable • Predictable

3. Daughter Parent Unstable Radioactive Isotope Stable Decay Product Nitrogen 14 (N14) Carbon 14 (C14) Uranium 238 (U238) Lead 206 (Pb206)

4. Half life: The time required for 1/2 of a parent material to break down to daughter (stable) material

5. Another look Half life remains constant, does not change if rock changes size

6. 100 0 50 50 25 75 12.5 87.5 6.25 93.75 3.125 96.875

7. Lets graph it!! 100% 50% 25% 4 1 2 3 Number of ½ lives

8. Radiometric Dating Knowing the amounts of parent and daughter atoms and the half life of the radioactive atoms, you can determine the age of the object

9. ESRT Page 1

10. Carbon 14 • Shorter ½ life • Used to date plants and animals of past 40,000 years - Carbon is incorporated into the cells of living organisms and begins to decay when the organism dies

11. Uranium 238 Used to date older rocks Has a larger half life

12. Half Life Practice Problems

13. How old are: A sample that has ½ C-14 and ½ N-14? How many half lives have gone by? If each element has ½ left then only one half life has gone by half like X 1 = 5700 X 1 = 5700 years

14. How old is A sample that has ¼ K-40 and ¾ Ar-40? K-40 has decayed how many half lives? half like X 2 = 1.9 X 109 X 2 = 3.8 X 109 2

15. How old is A sample that has ½ U-238 ½ Pb-206? U-238 has decayed how many half lives? half like X 1 = 4.5 X 109 X 1 = 4.5 X 109 1

16. How old are: • A sample that has 1/8 Rb-87 and 7/8 Sr-87? • A sample that has ¼ C-14 and ¾ N-14? • A sample that has ¾ C-14 and ¼ N-14?

17. What fraction remains of: • A 50 billion year old sample has ____ Rb-87 and ____ Sr-87. • A 2.6 billion year old sample has____ K-40 and ____Ar-40.