Evolution
Change in a kind of organism over time; process by which modern organisms have descended from ancient organisms.
Strata
layers of rock
natural selection
A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.
Adaptation
A trait that helps an organism survive and reproduce
Fitness
Ability of an organism to survive and reproduce in its environment
Fossil
A trace of an ancient organism that has been preserved in rock.
relative age
The age of a rock compared to the ages of rock layers
absolute age
The age of a rock given as the number of years since the rock formed.
homologous structures
Structures in different species that are similar because of common ancestry.
analogous structures
Body parts that share a common function, but not structure
vestigial structures
remnant of a structure that may have had an important function in a species' ancestors, but has no clear function in the modern species.
Phylogeny
Evolutionary history of a species