| A | B |
|---|
| 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 |
| punctuated equilibria | the theory that species evolve during short periods of rapid change |
| gradualism | the theory that evolution occurs slowly but steadily |
| variation | any difference between individuals of the same species |
| 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 |
| mold | a type of fossil formed when a shell or other hard part of an organism dissolves, leaving an empty space in the shape of that part |
| cast | a type of fossil when a mold becomes filled in with minerals that then harden |
| radioactive element | an unstable particle that breaks down into a different element |
| half-life | the time it takes for half of the atoms in a radioactive element to break down |
| fossil record | the millions of fossils that scientists have collected |
| extinct | a species that does not have any living members |
| petrified fossil | a fossil formed when minerals replace all or part of an organism |
| sedimentary rock | rock formed when layers of sediment harden over millions of years |
| fossil | the preserved remains or traces of an organism that lived in the past |
| 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 than that of other members of the same species |
| evolution | the gradual change in a species over time |
| species | a group of similar organisms that can mate with each other and produce fertile offspring |
| adaptation | a trait that helps an organism survive and reproduce |
