| A | B |
|---|
| 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 pressed and cemented together |
| Petrified fossil | A fossil in which minerals replace all or part of an organism |
| 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 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 scientist have collected |
| Extinct | A species that does not have any living members |
| Gradualism | The theory that evolution occurs slowly but steadily |
| Punctuated equilibria | The theory that species evolve during short periods of rapid change |
