1. Using the rock record to age date rock layers
Geologic Time
Using the rock record to age date rock layers

2. Age Dating
Geoscientists have devised a set of laws to help us understand (the “It’s so obvious” Laws)

3. Age Dating
Uniformitarianism- Earth’s processes have remained the same over time
(rock cycle, water cycle, climate, etc.)
If you know how a rock formed 1 million years ago…
then you know how the same type of rock formed 3 billion years ago

4. Age Dating Stratification rocks form in layers or strata
By looking at the surrounding layers, geoscientists can infer the relative age of a rock layer.

5. Relative Age Dating
Law of Superposition
oldest rocks on the bottom

6. Age Dating Law of Original Horizontality
layers originally deposited horizontally
If they are folded or tilted…
Then they have been disturbed

7. Age Dating Law of Cross-cutting Relationships
rock/faults that cut through rock layers must be younger than the layers

8. Age Dating Principle of Fossil Succession
fossils succeed each other in a definite order