What evidence exists that a Siberia to Alaska land bridge existed?
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M$2 Answers
http://www.youtube.com/watch?v=a1n47P2d1Fg&feature=player_embedded
In the Bering Strait Theory or Beringia theory, the bridge appeared as the ocean receded and vast amounts of water became tied up in the enormous glaciers of the last ice age that covered the continents. That exposed the broad continental shelves that today are covered by water at the Bering Strait, and created the land bridge that lasted between 70.000 BC to 11.000 BC.
According to "whyfiles.org":
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The bridge last arose around 70,000 years ago. For years, scientists thought it disappeared beneath the waves about 14,500 years ago, toward the end of the last ice age. Unfortunately, that was about 2,500 years before the first accepted date for human settlement in the new world.
So either the date was wrong, or the whole theory about the land bridge was bunk. Paleobiologist at the Institute for Arctic and Alpine Research at the University of Colorado have pinned the problem on the date.
They analyzed samples of sediment taken from beneath the Bering Strait with an advanced version of the carbon dating method that had produced the 14,500 years date. Their more accurate analysis showed that terrestrial plants and animals were living on the land bridge 11,000 years ago, meaning that the land bridge existed until after the oldest proven human settlements in the New World were started.
The area probably resembled today's North Slope of Alaska. It was a landscape with stunted willows, birches and small clumps of sedges. And why did it have no glaciers when ice as much as two miles thick was crushing much of the eastern two-thirds of North America? Because the regional climate was too dry. It was cold enough for glaciers, but without moisture, they can not form.
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Bering Strait Landscape.
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M$http://esp.cr.usgs.gov/research/alaska/alaskaC.html
http://www.bioone.org/doi/abs/10.1657/1523-0430%2807-076%29%5BAGER%5D2.0.CO%3B2
http://www.thefreelibrary.com/Ancient+American+site+identified+in+Alaska.-a013728829
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M$
1. 14,500 years ago, the Land bridge disappears
2. 12,200 years ago, human settleman forms
3. Based on the initial carbon dating, the human settlements could not have used the land bridge for migration.
4. New carbon dating puts the disappearance of the land bridge at 11,000 years ago
5. Land bridge theory remains viable
Right!