| A | B |
|---|
| Relative age | age of an object compared to the age of another object |
| Absolute age | true age of a rock or fossil |
| index fossil | fossil used to determine the relative age of rock layers |
| Half-life | length of time it takes for one-half the amount of a radioactive element to change into a stable element |
| Fossil | Remains or traces of an organism that lived long ago |
| Amber | hardened tree sap |
| Cast | mold filled with hardened sediments |
| mold | imprint or hollow in rock that is shaped like and made by an organism |
| Coprolite | fossil dung or the stomach contents of ancient animals |
| Geologic time scale | outline of the major divisions in earth's history |
| Precambrian | Oldest era in earth's history |
| Cenozoic | Present era |
| fossil fuel | natural fuel that was formed from the remains of living things. |
| Hydrocarbons | Compounds made up of the elements hydrogen and carbon |
