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The Bering land bridge was a land bridge roughly 1,000 miles (1,600 km) north to south at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages. It was not glaciated because snowfall was extremely light due to the southwesterly winds from the Pacific Ocean having lost their moisture over the fully glaciated Alaska Range. The grassland steppe including the land bridge and stretching for several hundred miles into the continents on either side has been called Beringia. It is believed that a small human population of at most a few thousand survived the Last Glacial Maximum in Beringia, isolated from its ancestor populations in Asia for at least 5,000 years, before expanding to populate the Americas sometime after 16,500 years ago, as the American glaciers blocking the way southward melted.[1][2][3][4] The Bering Strait, the Chukchi Sea to the north and the Bering Sea to the south, are all shallow seas (maps, right). During cycles of global cooling, such as the most recent ice age, enough sea water became concentrated in the ice caps of the Arctic and Antarctic that the subsequent drop in eustatic sea levels exposed shallow sea floors that have subsequently re-flooded. Other land bridges around the world have been created and re-flooded in the same way approximately 14,000 years ago, mainland Australia was linked to both New Guinea and Tasmania; the British Isles were an extension of continental Europe via the dry bed of the English Channel; and the dry basin of the South China Sea linked Sumatra, Java and Borneo to the Asian mainland. The rise and fall of global sea levels has exposed and submerged the bridging land mass called "Beringia" in several periods of the Pleistocene. The Beringian land bridge is believed to have existed both in the glaciation that occurred before 35,000 BP and during the more recent period 22,000-7,000 years Before Present. The strait reopened about 15,500 BP[5] and by c. 6000 BP the coastlines had assumed approximately their present configurations.[6]
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