| A | B |
|---|
| adaptation | a characteristic that helps an organism to survive in its environment or to reproduce |
| absolute dating | a technique used to deteremine the actual age of a fossil |
| branching tree | a diagram that shows how scientists think different groups of organisms are related |
| cast | a fossil that is a copy of an organism's shape formed when minerals seep into a mold |
| extinct | term used to describe a species that does not have any living members |
| evolution | the gradual change in a species over time |
| fossil | the preserved remains ot traces of an organism that lived in the past |
| fossil record | the millions of fossils that scientists have collected |
| gradualism | the theory that evolution occurs slowly but steadily |
| half-life | the time it takes for half of the atoms of a radioactive isotope sample to decay |
| homologous structure | body parts that are structurally similar in related species;provide evidence that the structures were inherited from a common structure |
| mold | a type of fossil formed when an organism burried in sediment dissolves, leaving a hollow area |
| natural selection | the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species |
| petrified fossil | a fossil formed when minerals replace all or part of an organism |
| punctuated equilibria | the theory that species evolve during short periods of rapid change |
| radioactive element | the process of determining the age of an object using the half-life of one or more radioactive isotopes |
| relative dating | a technique used to determine which of two fossils is older |
| species | a group of similar organisms whose members can mate with one another and produce fertile offspring in nature |
| variation | any differrence between individuals of the same species |
