1. Relative Time: Ages of events are placed in order of occurrence.
No exact date is identified.
Ex. WWI and WWII
I am the second child in my family.

2. Absolute Time: identifies the exact date of an event.
Ex. 65 Million Years Ago
1990

3. Finding age with relative time:
The Law of Superposition - in a sequence of undisturbed sedimentary rocks, the oldest rocks will be at the bottom.

4. 2. The law of cross-cutting relationships – anything that cuts across layers of rock is younger than the rocks that it has intruded into. This applies to faults and igneous intrusions.

5. 3. The law of included fragments - the fragments that make up a rock are older than the entire sample.

6. The Law of Folds or Tilts: tilts in rocks are younger than the rocks themselves.
Original Horizontality- Rocks are usually deposited flat and level.
Cole’s Law-
Thinly sliced cabbage.

10. Other Guidelines for figuring out a sequence:
Sedimentary rocks are usually formed under water.
Weathering and erosion usually happen above water (on dry land).

11. Contact metamorphism shows that the rock that was changed was there first when the intrusion happened.

12. Time for a worksheet
Sequence 1 & 2

13. Sequence 1: Uplift & Erosion
Limestone deposited
Sandstone deposited
Shale Deposited
Uplift
Erosion

14. Sequence 2: Faulting Limestone deposited Sandstone deposited
Shale deposited
Faulting

15. Time for another worksheet
Sequence 3 & 4

16. Sequence 3: Folding Limestone deposited Sandstone deposited
Shale deposited
Folding

17. By the way…
How can you tell if folding has gone so far as to flip the layers over?

18. Sequence 4: Igneous Intrusion
Limestone deposited
Sandstone deposited
Shale deposited
Igneous Intrusion
Note: contact metamorphism is the same event as the intrusion.

20. Formation of an unconformity

21. Layers are formed according to superposition.

22. Something happens to uplift the area
folding
faulting, etc.

23. Erosion wears away the uppermost layers

24. Area submerges and deposition begins again.
Here’s the
unconformity