| A | B |
|---|
| cast | a fossil formed when a fossil mold becomes filled |
| Cenozoic Era | about 65 million years ago to the present when recent life evolved on Earth |
| evolution | process of change over time |
| fossil record | fossils in sedimentary rock that tell the history of the earth |
| geologic time scale | chart that divides the earth's history into units of time |
| index fossil | a fossil of known age used to determine the relative age of other fossils |
| Mesozoic Era | about 65 to 250 million years ago during which reptiles were the major life form |
| mold | a fossil that is an imprint of an organism or its trace |
| Paleozoic Era | from 250 to 570 million years ago when many new life forms appeared and organisms first lived on land |
| petrified | replacement of tissues by minerals forming a stone |
| Precambrian time | the earliest time in the history of the earth |
| relative age | the age of a fossil or a sedimentary rock layer as compared to other fossils or sedimentary rock layers |
| shield | a region of Precambrian rock |
