Geology: Methods of Determining Rock Age

Study Notes

Catastrophism: Suggests Earth's landscapes formed rapidly through violent events.
Uniformitarianism: Earth's surface shaped by gradual, consistent processes similar to today's processes.
Relative Dating: Approximates rock age by comparing older and younger rock layers.
Stratigraphy: Studies rock layers and sequences.

Law of Superposition: Younger rocks are above older rocks in a sequence.
Original Horizontality: Rocks were originally laid down horizontally, even if tilted now.
Lateral Continuity: Rock layers extend laterally even if eroded in some areas.
Cross-Cutting Relationships: A rock that cuts through another is younger than the rock it cuts.
Inclusion: Fragments within a rock layer are older than the enclosing rock.

Paraconformity: Parallel rock layers indicating continuous deposition.
Disconformity: Irregular boundary caused by erosion and pause in deposition.
Nonconformity: Sedimentary rocks deposited on igneous or metamorphic rocks.
Angular Unconformity: Younger rocks deposited on tilted and eroded older rocks.

Fossil Types:
- True Form Fossils: Actual organism or parts.
- Mold Fossils: Imprints left by organisms.
- Cast Fossils: Minerals filling mold fossils.
- Trace Fossils: Evidence of organism activity (e.g., footprints, burrows).
Geologic Time Units:
- Eon: Largest division (hundreds of millions to billions of years).
- Era: Subdivision of an eon (tens to hundreds of millions of years).
- Period: Subdivision of an era (tens of millions of years).
- Epoch: Subdivision of a period (several million years).
Hadean Eon: Early Earth history, frequent volcanic eruptions, asteroid impacts.
Cenozoic Era ("Age of Mammals"):
- Tertiary Period: Giant rhinos, elephants, lions, saber-tooth cats.
- Quaternary Period ("Age of Humans"): Homo erectus appeared in Africa.
Cretaceous Period: Dinosaurs went extinct.