| A | B |
|---|
| species | a group of similar organisms that can mate w/ each other and produce fertile offspring |
| adaptation | a trait that helps an organism survive and reproduce |
| evolution | the gradual change in a species over time |
| 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 |
| 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 | rock formed when layers of sediments harden over millions of years |
| petrified fossil | a fossil formed when minerals replace all or part of an organism |
| mold | a hollow space in sediment in the shape of an organism or part of an organism |
| cast | a type of fossil that forms when a mold becomes filled in with minerals that then harden |
| 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 in a radioactive element to break down |
| fossil record | the millions of fossils that scientists have collected |
| extinct | no members of that species is still alive |
| gradualism | the theory that evolution occurs slowly but steadily |
| punctuated equilibria | the theory that species evolve during short periods of rapid change |
