1. Time is not part of rock cycle, but is implied
Example: a granite could be weathered and the particles
eventually become part of a sandstone. The sandstone
could later be metamorphosed to become a quartzite.
How fast these events happen would determine
what ages the rocks were.

5. RELATIVE DATING OF GEOLOGIC EVENTS / MATERIALS: PRINCIPLES
Superposition
Original Horizontality
Cross-cutting relationships

6. Superposition

8. Original Horizontality

9. original horizontality

10. Erosion and creation of unconformity

12. Cross-cutting relationships

13. Deposition of 1 – 5 Superposition
Event Principle
Deposition of 1 – 5 Superposition
Folding of 1 – 5 Original Horizontality
Erosion Superposition / Cross-cutting
Deposition of 7 – 9 Superposition
time

16. Figure 18.4 .5 Layer E Layer D Layer C Layer B Layer A Layer F Layer H
Layer G
Layer E
Layer D
Layer C
Layer B
Layer A
Figure 18.4 .5

20. Uranium-238
Unstable parent
Rn-222
Radon gas
Lead 206
Stable daughter

21. Example radioactive decay pairs
Parent
Daughter
Half life (years)
Uranium-238
Lead-206
4.5 billion
Uranium-235
Lead-207
713 million
Rubidium-87
Strontium-87
47 billion
Carbon-14
Nitrogen-14
5,370

22. Figure 18.14

23. radiometric dating – example 1
A granite is collected and analyzed
Contains 50% U-235 and 50% Pb-207
Half-life of U-235 is 713 million years
How old is the granite?

24. radiometric dating – example 1
Refer to Figure 18.14
50% parent, 50% daughter corresponds to 1 half-life
Half-life of U-235 is 713 million years
Thus, granite is 713 years old

25. radiometric dating – example 2
A granite is collected and analyzed
Contains 2 micrograms of U-235 and 6 micrograms of Pb-207
Half-life of U-235 is 713 million years
How old is the granite?

26. radiometric dating – example 2
8 micrograms of parent + daughter
2/8 micrograms = 1/4 = 25% U-235
6/8 micrograms = 3/4 = 75% Pb-207
Refer to Figure 18.14
25% parent / 75% daughter corresponds to
2 half lives.
Half-life of U-235 is 713 million years
Thus, granite is 2 x 713 = 1,426
million years old = 1.4 billion yrs.
What if U-235 = 75%, Pb-207 = 25%?

29. Europe
Modern humans
Present time
Asia
13,000 years
Archaic humans
incl. Neanderthals
33,000 years
Small Archaic
Humans
95,000 years
Evolution of humans
~3 million years ago
Africa

31. Correlation: establishing equivalence
between rock layers that were once
continuous