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Deep Time

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How Long Do Collisions Take?

The Sun takes two hundred and fifty million years to go once
around the Milky Way. A galaxy collision might take four times
as long, or one billion years.

For comparison:
-- Recorded human history spans about five thousand years.
-- Human beings evolved about half a million years ago.
-- The dinosaurs became extinct about sixty million years ago.
-- Fish evolved about five hundred million years ago.
-- Life evolved about four billion years ago.
-- The Earth and Sun are about five billion years old.
-- The Universe is about thirteen billion years old.

Joshua E. Barnes (
Last modified: October 27, 2000