| A | B |
|---|
| fossil | trace of a long-dead organism |
| sediment | dust, sand or mud |
| mold | an imprint in rock in the shape of an organism |
| cast | rocklike model of the organism |
| law of superposition | successive layers or rock or soil deposited on top of one another by wind or water |
| stratum | lowest and oldest layer in a cross section of earth |
| relative age | a fossil is younger or older than another fossil |
| absolute age | could be estimated from radiological evidence |
| extinct | a species of organisms appeared, existed for awhile and then dissapeared |
| mass extinction | brief perriod during which large numbers of species disappeared |
| biogeography | study of the geographicaal distribution of fossils and living organisms |
