| A | B |
|---|
| Law of Included Fragments | Bits of sediments incorporated into another rock are older than the rocks they get “stuck” in. |
| Uniformitarianism / Law of Uniformity of Process | Earth processes happening today are similar to the way things happened in the past. |
| Law Of Superposition | In layers of undisturbed rock, the oldest are on the bottom, and the younger rocks are on top. |
| Law of Cross Cutting Relationships | A dike or other mass of rock that cuts across other rock layers is younger than the rock layers it cut through. |
| Unconformity | A “break” in the rock record. Where the surface between one layer of rock may have been left out to weather & erode for a long time before the layer above was formed. |
| Relative Time / Age | You can tell what is older or younger but not how old. |
| Absolute Time / Age | You can tell exactly how old something is. |
| Radioactive Dating | A ratio of parent and daughter isotopes with in a sample is used to determine how old the sample is. Different isotopes are used depending on what ballpark age you think the material is. |
| Index Fossils | These are special types of fossils that were only around at certain times in the Earth’s history. So if you find this type of fossil, it must be in rock from that time. |
| Correlation | The matching of rock layers from one area with the same rock layer in another area. Sometimes fossils are used to do this. |
| Mass Extinction | When a large numbers of organisms becomes extinct in a relatively "short" period of time. |
| 4.6 Billion Years | Age of the Earth as determined by Geologists. |
| Eon, Era, Period, Epoch | "Periods" of geologic time. |
| Cenozoic | Era of Mammals. We currently live in this time era. |
| Mesozoic | Era of reptiles and dinosaurs. Ended 65 MYA. |
| Paleozoic | Age of "Old Life", the era before the dinosaurs. (600-225 MYA) |
| Precambrian | Considered by some to be an era of geologic time before 600 MYA. |
