Friday's forecast doomsday is one of many visions predicting the end of the world through history.
Some believe the world is coming to an end Friday -- on 12/21/12 -- which is when an important phase on the ancient calendar of the Mayan people terminates. Here's a look back at just some of the failed doomsday predictions through human history.
What's behind the tradition of turning our clocks ahead each spring?
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