| A | B |
|---|
| Fossils | Evidence such as the remains, imprints, or traces of once-living organisms preserved in rocks |
| Petrified Remains | Hard and rocklike in which the molecules have been replaced one by one by minerals |
| Carbonaceous Film | Process of chemically changed plant material |
| Mold | Cavity in the rock |
| Cast | Sediments may fill in the cavity, harden into rock |
| Trace Fossils | Fossilized tracks and other evidence of animal activity |
| Index Fossils | Fossils that lived a short period of time and were widespread |
| Law of Superposition | States that in a series of rock layers, the oldest rocks are on the bottom and the youngest are on top |
| Relative Dating | Determines age by the position of rocks in a sequence |
| Unconformities | Gaps in the rock record |
| Half-life | Time it takes for one-half of the atoms in an isotope to decay |
| Principle of Uniformitarianism | States that earth's processes today are the same as those in the past |
