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Geologic Time
Geology
| Term | Definition |
|---|---|
| Geologic Time Scale | Contains information about important events in earth's history. Divisions of time are determined by when major changes happened on earth. |
| Eon | Largest unit of geologic time. |
| Era | Second largest unit of geologic time. |
| Period | Second smallest unit of geologic time. |
| Epoch | Smallest unit of geologic time. |
| Absolute Age | The approximate age of a rock or fossil in years. |
| Relative Age | The age of a rock or fossil compared to other rocks or fossils (older / younger) |
| Half Life | The time it takes for half of the radioactive, parent atoms to decay (change) to stable daughter atoms. |
| Relative Dating | Using the law of superposition, the law of cross cutting, and index fossils in order to compare the age of rocks or fossils (older / younger) |
| Absolute Dating | Using radiometric dating (half life) to determine the approximate age of a rock or fossil in years |
| Law of Superposition | In undisturbed layers of sedimentary rock, the oldest rocks are at the bottom |
| Law of Crosscutting | When a geologic feature (intrusion, erosion, fault) cuts through a rock layer, it is younger than the rock layer it cuts through |
| Index Fossil | Fossil of an organism that lived for a relatively short time, but was widespread. |
| Trilobite | An example of an index fossil |