| A | B |
|---|
| species | a group of similar organisms whose members can mate with one another and produce fertile offspring |
| adaptation | a characteristic that helps an organism survive in its environment or reproduce |
| evolution | the gradual change in a species over time |
| scientific theory | a well-tested concept that explains a wide range of observations |
| natural selection | the process by which individuals that are better adapted to their environment are more likely to survive and reproduce that other members of the same species |
| variation | any difference between individuals of the same species |
| fossil | the preserved remains or traces of an organism that lived in the past |
| sedimentary rock | a type of rock that forms when particles from other rocks or the remains of plants and animals are presses and cemented together |
| petrified rock | a fossil in which minerals replace all or part of an organsim |
| mold | a fossil formed when an organsim buried in sediment dissolves, leaving a hollow area |
| cast | a fossil that is a copy or an organism's shape, formed when minerals seep into a mold |
| relative dating | a technique used to determine which of two fossils is older |
| absolute dating | a technique used to determine the actual age of a fossil |
| radioactive element | an unstable particle that breaks down into a different element |
| half-life | the time it takes for half of the atoms of a radioactive element to decay |
| fossil record | the millions of fossils that scientists have collected |
| extinct | a species that does not have any living members |
| gradualism | the theory that evolution occurs slowly but steadily |
| punctualed equilibria | the theory that species evolve during short periods of rapid change |
| homologous structure | body parts that are structurally similar in related species; provide evidence that the structures were inherited from a common ancestor |
| branching tree | a diagram that shows how scientists think different groups of organisms are related |
