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7 Cards in this Set
- Front
- Back
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Geologic Time Scale |
A record of Earth's history from its origin 4.6 billion years ago to the present. |
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Eon |
The largest time unit; encompasses the others. |
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Precambrian |
unit of geologic time consisting of the first three eons during which Earth formed and became hospitable to earth. |
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Era |
Second longest time unit in the geologic time scale, measured in tens to hundreds of millions of years, and defined by differences in life forms that are preserved in rocks. |
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Period |
third longest time unit in the geologic time scale, measured in tens of millions of years. |
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Epoch |
time unit in the geologic time scale, smaller than a period, measured in hundreds of thousands to millions of years. |
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Mass Extinction |
occurs when an unusually large number of organisms disappear from the rock record at about the same time. |
