| A | B |
|---|
| petrified | bones and hard structures replaced by minerals |
| mold | empty space left as organism decays |
| cast | replica or organism formed when mold is filled in |
| imprint | living material falls into sediment, covered quickly, forms impression |
| trace | footprints, trails or burrows |
| in amber or ice | entire organism trapped |
| Precambrian | oldest organisms appeared here |
| Cenozoic | shortest era, we are in it now |
| Paleozoic | consists of 6 periods, much marine life present |
| Mesozoic | Age of dinosaurs, more mammals and modern birds appeared |
