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