1. Radioactive dating

2. III. Radioactive Dating
A. Used to find ABSOLUTE age in years.
B. Radioactive ISOTOPES in rocks DECAY away at a predictable rate.

3. III. Radioactive Dating
1. Carbon-14 – Used to date RECENT, ONCE LIVING things.
Decays into Nitrogen-14

5. III. Radioactive Dating
2. Uranium-238 – Used to date very old rocks. Decays into Lead-206.

6. Half Life
C. The amount of time it takes for HALF of the radioactive isotope to DECAY is called its HALF LIFE.
1. Half life DOES NOT CHANGE. (That’s why it’s on the ESRT!)

8. Radioactive isotopes decay from the “Parent” material
into the “Daughter Product”.
Daughter Product
Original
“Parent” Material

9. Each half-life, the amount of atoms gets cut in half.

10. One half-life.

11. Two half-lives.

12. Three half-lives.

13. Four half-lives.

14. Don’t worry about the last atom
Don’t worry about the last atom. You start with so many trillions that you never really get there. (It will just decay and then they’re all gone.)

15. Since you don’t know how many atoms you started with, a ratio between parent to daughter will tell you how many half-lives have gone by.
100% parent
0% daughter
0 half lives

16. One half-life.
50% parent
50% daughter
1 half-life

17. Two half-lives.
25% parent
75% daughter
2 half-lives

18. Three half-lives.
12.5% parent
87.5% daughter
3 half-lives

19. Four half-lives.
6.25% parent
93.75% daughter
4 half-lives