1. Radioactive dating

2. Unstable! (radioactive)
Unstable isotopes ‘decay’ by various nuclear processes.
Each such isotope is characterized by a half life:
Stable!
Unstable! (radioactive)

3. Stable!
b decay t½ = 5,730 years.

4. start The carbon-14 decay is characterized by a
‘half life’ t½ = 5,730 years.
start

5. The carbon-14 decay is characterized by a
‘half life’ t½ = 5,730 years.

6. The carbon-14 decay is characterized by a
‘half life’ t½ = 5,730 years.

7. The carbon-14 decay is characterized by a
‘half life’ t½ = 5,730 years.

8. The carbon-14 decay is characterized by a
‘half life’ t½ = 5,730 years.

9. The carbon-14 decay is characterized by a
‘half life’ t½ = 5,730 years.

11. radio-carbon dating

12. Air

13. cosmic rays
Air

14. cosmic rays
Air

15. cosmic rays
Air

16. Carbon dating

17. Carbon dating
nothing

18. Carbon dating
time passes:

19. Carbon dating
mass spectrometer

20. Carbon dating
mass spectrometer

21. Carbon dating

23. dating rocks

24. Stable!

25. Stable!
Another (naturally occurring) strontium isotope

26. Strontium isotopes chemically identical!
Molten rock, t = 0
Strontium isotopes chemically identical!

27. rock crystallizes, t = 0
mineral A
mineral B

28. rock crystallizes, t later
mineral A
mineral B

29. Number of Rb’s that’ve decayed to 87Sr since t = 0

33. 13
mineral A
mineral B 6 4 11

34. Slope =