| A | B |
|---|
| extinction | elimination of a species from Earth |
| punctuated equilibrium | theory that states that speciation occurs suddenly and rapidly followed by long periods of little evolutionary change |
| adaptive radation | process by which one species evolves and gives rise to many descendant species that occupy different ecological niches |
| relattive dating | estimate of the age of a fossil based on the location of fossils in strata |
| isotope | form of an element that has the same number of protons but a different number of neutrons as another element |
| half-life | amount of time it takes for half of the isotope in a sample to decay into its product isotope |
| index fossil | fossil of an organism that exsted during only specific spans of geologic time across large geographic areas |
| geologic time scale | time scale representing the history of the Earth |
| mass extinction | •Many species becoming extinct at about the same time. |
| theory | •a well-substantiated explanation of some aspect of the natural world |
| macroevolution | •evolution on a large scale extending over geologic era and resulting in the formation of new taxonomic groups |
