Remains of organisms preserved in the earth.
One fossil is compared to another fossil.
Tells you the exact age of a fossil using radioactive elements.
When large numbers of species become extinct in a short time.
When species change over time.
Members of a species that are best suited to their environment survive and reproduce at a higher rate than other members of the species.
Within a species there are natural differences in traits.
Any inherited trait that gives an organism an advantage in its particular environment.
The evolution of new species from existing species.
An early form of an organism from which late forms descend.
Physical structures that were fully developed and functional in an ancestral group of organisms, but are reduced and unused in later species.