Dating Rock Layers. How to tell how old the layers of rock are. What is Age?. There are 2 kinds: Absolute Age – The number of years since the rock formed. (150 million years old, 10 thousand years old.)
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How to tell how old the layers of rock are.
1. Law of Superposition
2. Extrusion & Intrusion
In horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.
More rock layers are deposited on top of the extrusion.
First of all, which rock layer is the oldest?
What is this called?
Faults move over time causing the rock layers to move.
As more time goes by, more rock layers are added on top. Making aging the rock layers difficult.
Geologists must then label each of the rock layers. This can be tough because they weren’t around to see the whole process occur.