As a unit of time equal to a billion years.

As a specific number of years determined by fossil evidence.

As a subdivision of a period.

As a division of time within an eon.

Only the strongest organisms live

Organisms best suited to their environment survive and reproduce

The largest animals always survive

All organisms survive equally

The study of continental drift.

The study of glacier sediments.

The study of folding and faulting of the Earth's crust.

The study of plant and animal fossils.

The survival and reproduction of well-adapted individuals.

The passing on of genes to offspring.

The physical changes in organisms over generations.

The process of genetic variation

Adaptations become less important.

Organisms become less diverse.

Physical appearance and habits of organisms change.

Genetic variation increases.