| A | B |
|---|
| Overproduction | the struggle among living things for limited resources |
| competition | the struggle among living things for limited resources |
| variation | the difference between individuals of the same species |
| speciation | when one species evolves from another |
| gradualism | evolution occurs slowly and steadily |
| punctuated equilibria | species evolve during short periods of rapid change |
| homologus structures | provide evidence of how species are related and of how they evolved from a common ancestor |
| branching tree | a diagram that shows how scientists think different groups of organisms are related |
| mold | a fossil formed when an organism buried in sediment dissolves, leaving a hollow area |
| cast | a fossil that is a copy of an organism's shape, formed when minerals seep into a mold |
| relative dating | a technique used to determine the actual age of a fossil |
| absolute dating | a technique used to determine the actual age of a fossil |
| half-life | the time it takes for half of the atoms in a sample to decay |
| fossil record | the millions of fossils that scientists have collected |
| fossil | the preserved remains or traces of an organism that lived in the past |
| extinct | a species that does not have any living members |
