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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 |