| A | B |
|---|
| variations | differences in species based on traits |
| adaptations | trait/behavior; helps an organism survive and reproduce |
| mold fossil | cavity in rock; has shape of organism |
| cast fossil | fossil in shape of an organism |
| petrified fossil | plant or animal remains have been turned to rock |
| preserved fossil | organism or part of organism is trapped in tar, sap, ice |
| carbonized fossil | thin carbon imprint of a fossil on a rock |
| index fossils | fossils of organisms that lived for a short period of time over large area |
| Precambrian | oldest and longest geologic time period |
| Paleozoic Era | Oldest era; organisms developed hard parts |
| Mesozoic Era | middle era; reptiles dominant |
| Cenozoic Era | present era; great diversity of life forms |
| periods | subdivisions of eras |
| Cambrian Period | First period of geologic time |
| Quaternary Period | our present period of geologic time |
| epoch | subdivision of a period |
| Holocene epoch | our present epoch of geologic time |
| relative age | no numbers; comparision of older and younger |
| strata | rock layers |
| Law of Superposition | in undisturbed rock, oldest layers are at the bottom |
| trace fossils | fossilized tracks or other evidence of an organism |
| trilobite | hard shelled; Paleozoic; index fossil |
