| A | B |
|---|
| fossil | preserved remains or traces of a dead organism |
| sedimentary rock | rock formed when sediments harden over many years |
| petrified fossil | fossil formed when minerals replace remains of an organism |
| mold | fossil formed when a hard part of an organism dissolves leaving empty space |
| cast | fossil formed when a mold becomes filled with hardened minerals |
| relative dating | using rock layers to determine age of fossils |
| absolute dating | using radioactive elements to determine the age of a fossil |
| radioactive element | an element that is unstable and breaks apart over time |
| half-life | time needed for half the atoms in a sample to break down |
| fossil record | the millions of fossils that scientists have collected |
| extinct | a species without any living members |
| gradualism | theory that evolution occurs slowly but steadily |
| punctuated equilibria | theory that species evolve during short periods of rapid change |
| variation | the differences in traits among individuals |
| species | group of similar organisms that can mate with each other |
| adaptation | a trait that helps an organism to survive |
| scientific theory | a well-tested concept that explains many observations |
| natural selection | process by which better adapted organisms survive and reproduce |
| artificial selection | process where humans choose which parents reproduce |
| transitional species | close relative of two species that shows an intermediate form between the ancestor and its descendants |
| embryo | an unborn/unhatched offspring that is in the process of forming and developing |
| homologous structures | parts of related organisms that are formed similarly but may have different jobs |
| analogous structures | parts of unrelated organisms that perform the same job |
| vestigial structure | structure with no current function in one organism, but, with a definite structure and function in another species |
| biogeography | study of the past and present geographical range of organisms |
| biochemistry | the chemicals and their functions in living things |
