1. Relative Vs. Absolute Dating of Rocks

2. Relative Age Dating of Rocks
Put these people in order from youngest to oldest. B A C D

3. Relative age Dating of Rocks
Can you tell the exact ages of these people?

4. Dating
Relative age dating- places the ages of rocks and the events that formed them in order, but without dates.
by comparing one rock layer to another
no specific date!

5. Principle of Uniformitarianism
Uniformitarianism- the processes happening today are the same ones that happened millions of years ago
This is why we can compare rock layers!

6. Relative age Dating of Rocks
Principle of Superposition – in an undisturbed rock sequence, the older rocks are at the bottom and each successive layer is older than the layer above it.

7. Inclusions
Inclusions- are pieces of one rock unit that are within another rock unit.
Example) Pieces of granite embedded in shale.
The rock containing the inclusions has to be older than the rock that gave the inclusion.

8. Intrusions
Intrusions are pieces of one rock unit that cross cut other layers.
Law of cross- cutting relationship: If P “intruded” rock layers Q, O and N, P must be younger than Q, O and N

9. Principle of Inclusions

10. Inclusions and Intrusions

11. Step 1: Deposition – horizontal

12. Fig
Step 1 (cont.): Deposition – horizontal

13. Fig
Step 2: Intrusion of granite

15. Fig. 08.05 Step 3: Tilting of layers
Step 4: Erosion to create unconformity

16. Fig
Step 5a: Submergence and deposition of new layers

17. Fig
Step 5b: ….. possibly additional formations

18. Fig
Step 6: Intrusion Through weakness of layers

19. Step 7: Erosion of Layers-- Unconformity

20. Fig
Step 8: Erosion due to stream

22. Folding
Crustal activity can cause the crust to look wavy.

23. Folding
Did F form after/before D folded? A B C D E F G

24. Unconformity
An unconformity is something that is out of the ordinary in rock layer formation. Unconformity at line XY
The bottom layers were tilted by crustal movement. X Y

25. Relative Age Dating Excercise
Unconformity!
Intrusion!
Inclusion!
If layer L is 65 million years old, and layer H is 35 million years old, what is a possible age of intrusion P? What is the possible age of J?

26. Absolute age dating of rocks
Determine the actual age (in millions of years) of a rock, fossil or other object.
Use the decay rate of radioactive isotopes within rocks and fossils.
Radioactive materials emit particles at a constant rate.

27. Absolute Age Dating

28. Absolute Age Dating of Rocks
Radiometric dating- depending on what elements are present in the fossils we can tell exactly how old the fossil is.

29. Half Life
Half Life- The time it takes for one element to lose half of its particles.

30. Compare and Contrast

31. Index Fossils
Remains of a plant or an animal that can be used by geologists to correlate rock layers over a large area.
Can also be used to date a particular fossil.
Characteristics
Easily recognized
Abundant
Widely Distributed
Alive for a short period of history