| A | B |
|---|
| Trace fossil | imprints left in rocks by animals, footprints |
| Half-life | time it takes for half of the mass of a radioactive isotope to decay |
| Relative Age | age of object in relation to another object by position in rock record |
| Paleontology | study of fossils |
| Unconformity | break in the geologic record caused by erosion |
| Natural selection | survival of the fittest |
| Absolute age | numeric age of an object determined by radioactive decay |
| Superposition | law stating that older rock layers are below younger rock layers |
| Stromatolite | fossilized blue-green algae that lived in the Precambrian era |
| Fossil | remains of an organism that lived long ago |
