Relative Dating
Geologist interpret Earth’s history by studying sedimentary rocks
Interpreting Earth’s History
1. Rock record gives evidence of geological event
(earthquakes, volcanoes, erosion) and life forms
of the past (dinosaurs)
2. Processes we find on Earth today also worked in
the past
3. Earth is very old and changes over geologic time
Uniformitarianism
Physical Laws
Chemical Laws
Biological Laws
Steno’s Laws
Law of superposition (each layer is older than the
one above it)
Principle of Original Horizontality (layers of
sediment are deposited in a horizontal position
Principle of Cross-Cutting Relationships (a fault
cuts through rock or magma intrudes then the
fault or intrusion is younger than the rock it cuts
through)
Law of Superposition
Principle of Original Horizontality
Principle of Cross-Cutting Relationships