Geologic History

The study of rock layers

• Stratigraphy

• Cross-cutting relationships

• Absolute dating

• Faunal succession

Younger events "cut across" older events

• Stratigraphy

• Cross-cutting relationships

• Absolute dating

• Faunal succession

Using tree rings, shell rings, or radioactive dating to determine the age of an unknown object

• Stratigraphy

• Cross-cutting relationships

• Absolute dating

• Faunal succession

Younger fossils are seen above older fossils in the fossil record - organisms that go extinct will not be seen again.

• Stratigraphy

• Cross-cutting relationships

• Absolute dating

• Faunal succession

The process of estimating the age of a fossil or rock layer based upon what can be seen around it.

• Relative dating

• Law of Original Horizontality

• Law of Superposition

• Evolution

If rock layers are folded or upturned, a geologic event has occurred.

• Relative dating

• Law of Original Horizontality

• Law of Superposition

• Evolution

Younger rock layers can be seen above older rock layers

• Relative dating

• Law of Original Horizontality

• Law of Superposition

• Evolution

Change over time

• Relative dating

• Law of Original Horizontality

• Law of Superposition

• Evolution

Rock layers are lifted, younger layers are deposited on top.

• Angular unconformity

• Nonconformity

• Disconformity

• Index fossil

Soft rock layer is eroded, new rock layer is deposited on top.

• Angular unconformity

• Nonconformity

• Disconformity

• Index fossil