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Shrinking of the Bering land bridge

The Bering land bridge joined present-day Alaska and eastern Siberia at times during the Pleistocene ice ages.

Its greatest extension was about 1,000 miles (1,600 km) north to south. It was not glaciated because snowfall was extremely light the southwesterly winds from the Pacific Ocean lost their moisture over the fully glaciated Alaska Range.

The grassland steppe, including the land bridge, that stretched 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 ice age in Beringia. It was isolated from populations in Asia for at least 5,000 years. Sometime after 16,500 years ago, it started to populate the Americas when the American glaciers that blocked the way southward melted.[1][2][3][4]


Berengia -Wisconsin glaciation
Berengia - deglaciation period
Berengia - present day

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 Antarctica 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]

Human habitation

The Bering land bridge is significant for several reasons, not least because it is believed to have enabled human migration to the Americas from Asia about 25,000 years ago.[7] A study by Hey[8] has indicated that of the people migrating across this land bridge during that time period, only 70 left their genetic print in modern descendants.

Further reading

  • Pielou, E. C., After the Ice Age : The Return of Life to Glaciated North America (Chicago: University of Chicago Press) 1992
  • Hey, Jody, 2005. "On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas" in Public Library of Science Biology 2005 May 24;3(6):e193


  1. Goebel, Ted; Waters, Michael R.; O'Rourke, Dennis H. (2008). "The Late Pleistocene Dispersal of Modern Humans in the Americas". Science 319 (5869): 1497–1502. doi:10.1126/science.1153569 .
  2. Fagundes, Nelson J. R.; et al. (2008). "Mitochondrial Population Genomics Supports a Single Pre-Clovis Origin with a Coastal Route for the Peopling of the Americas". American Journal of Human Genetics 82 (3): 583–592. doi:10.1016/j.ajhg.2007.11.013 .
  3. Tamm, Erika; et al. (2007). "Beringian Standstill and Spread of Native American Founders". PLoS ONE 2 (9): e829. doi:10.1371/journal.pone.0000829 .
  4. Achilli, A.; et al. (2008). "The Phylogeny of the Four Pan-American MtDNA Haplogroups: Implications for Evolutionary and Disease Studies". PLoS ONE 3 (3): e1764. doi:10.1371/journal.pone.0001764 .
  5. E.C. Pielou, After the Ice Age: The Return of Life to Glaciated North America (Chicago: University of Chicago Press) 1991:19 and note.
  6. Isostatic rebound has continued to raise some sections of coast.
  7. National Geographic. "Atlas of the Human Journey." 2005. May 2, 2007
  8. Hey, Jody (2005). "On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas". PLoS Biology 3 (6): e193. doi:10.1371/journal.pbio.0030193 .

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