|
 absolute age | exact age in years, of a rock or other object, such as a fossil |
| half-life | length of time required for half of the radioactive atoms in a sample to decay |
| index fossils | remains of species that existed on earth for a reletively short period of time,were abundant, and were widespread geographically |
| Principle of Superposition | States that in undisturbed rock layers, the oldest rocks are on the bottom and the rocks become progressively younger toward the top. |
| unconformity | A surface that represents a break in the rock record, caused by erosion or lack of deposition |
| igneous intrusion | magma cutting through formed layers of sedimentary rock that then cools and hardens ( younger than the layers it cuts across) |
| Law of cross cutting | Any feature that cuts across a rock or body of sediment must be younger than the rock or sediment that it cuts across |
| outcrop | part of a rock or mineral formation that is exposed at the surface of the ground ( not buried ,can see it) |
| Principle of Uniformitarianism | Processes that act upon the Earth today are the same processes that have acted upon it in the past. The present is the key to the past. |
| relative age | approximate age of a rock or something else when compared to other rocks or things. |