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The galactic year, also known as a cosmic year, is the duration of time required for the solar system to orbit once around the center of the Milky Way galaxy.[1] Estimates of the length of one orbit range from 225 to 250 million "terrestrial" years. [2]
The galactic year provides a conveniently "graspable" unit for thinking about cosmic and geological time periods. (By contrast, a "billion-year" scale does not allow for useful discrimination between geologic events, and a "million-year" scale requires some rather large numbers.) [3]
[edit] Timeline of earth's history in galactic years
In this list, 1 galactic year (GY) = 225 million years
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