Goahti

More than 50,000 years ago, North America was connected to Asia by a land bridge that is now largely underwater.

Bering Land Bridge

This land bridge was once thousands of miles wide. It was part of a migration route for animals, and plants whenever water levels fell low enough to expose the land bridge. Yet people did not make the crossing until the last Ice Age, more than 13,000 years ago, according to archaeological and genetic evidence.
A recent study indicates that the Bering Land Bridge existed until about 11,000 years ago, at which time it was covered over again by the Chukchi Sea and the Bering Sea.
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So, why the delay? Maybe our ancestors took a while to realize the value of the poop along their path!

Scientists have long blamed the delay on cold weather and a lack of fuel for heating and cooking. Now, researchers suggest that our ancestors eventually learned to survive cold-weather travel by taking advantage of all the dung lying around. Back then, this route from Russia to Alaska was bursting with big plant-eating animals, like bison, mammoths, horses, and wooly rhinoceroses. With animals comes waste. So there was plenty of dried dung to fuel the trip. Even modern-day Tibetans, who live at an average (cold!) altitude of 16,000 feet (4,900 m), survive by heating their tents and cooking their food by burning Yak dung!

Source courtesy of: nps.seeamerica.org/pmgr?parkId=37, sciencenewsforkids.org/articles/20030813/Note3.asp, usparks.about.com/od/nationalparksus/a/Bering.htm

Photo courtesy of: nps.seeamerica.org/pmgr?parkId=37