The Bering land bridge was a
land bridgeroughly 1,000 miles (1,600 km) north to south at its greatest extent, which joined present-day Alaskaand eastern Siberiaat various times during the Pleistocene ice ages. It was not glaciated because snowfall was extremely light due to the southwesterly winds from the Pacific Oceanhaving lost their moisture over the fully glaciated Alaska Range. The grassland steppeincluding the land bridge and stretching for several hundred miles either side of it has been called Beringia. It is believed that a small human population of at most a few thousand survived the last ice age 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. cite journal | last = Goebel | first = Ted | authorlink = | coauthors = Waters, Michael R.; O'Rourke, Dennis H. | year = 2008 | month = | title = The Late Pleistocene Dispersal of Modern Humans in the Americas | journal = Science | volume = 319 | issue = 5869 | pages = 1497–1502 | doi = 10.1126/science.1153569 | url = | accessdate = | quote = ] cite journal | last = Fagundes | first = Nelson J. R. | authorlink = | coauthors = "et al." | year = 2008 | month = | title = Mitochondrial Population Genomics Supports a Single Pre-Clovis Origin with a Coastal Route for the Peopling of the Americas | journal = American Journal of Human Genetics| volume = 82 | issue = 3 | pages = 583–592 | doi = 10.1016/j.ajhg.2007.11.013 | url = | accessdate = | quote = ] cite journal | last = Tamm | first = Erika | authorlink = | coauthors = "et al." | year = 2007 | month = | title = Beringian Standstill and Spread of Native American Founders | journal = PLoS ONE| volume = 2 | issue = 9 | pages = e829 | doi = 10.1371/journal.pone.0000829 | url = | accessdate = | quote = ] [ cite journal | last = Achilli | first = A. | authorlink = | coauthors = "et al." | year = 2008 | month = | title = The Phylogeny of the Four Pan-American MtDNA Haplogroups: Implications for Evolutionary and Disease Studies | journal = PLoS ONE | volume = 3 | issue = 3 | pages = e1764 | doi = 10.1371/journal.pone.0001764 | url = | accessdate = | quote = ]
Bering Strait, the Chukchi Seato the north and the Bering Seato the south, are all shallow seas ("map, right"). During cycles of global cooling, such as the most recent ice age, enough sea water became concentrated in the ice caps of the Arcticand Antarcticthat the subsequent drop in eustatic sea levels exposed shallow sea floors. Other land bridges around the world have been created and re-flooded in the same way: approximately 14,000 years ago, mainland Australiawas linked to both New Guineaand Tasmania; the British Isleswere an extension of continental Europevia the English Channel; and the dry basin of the South China Sealinked Sumatra, Java and Borneoto the Asian mainland.
The rise and fall of global sea levels has exposed and submerged the land bridge in several periods of the
Pleistocene. The bridging land mass called "Beringia" is believed to have existed both in the glaciationthat occurred before 35,000 BC and during the more recent period 22,000-7,000 years ago. By c. 4000 BC the coastlines had assumed approximately their present configurations.
Beringia constantly transformed its
ecologyas the changing climate affected the environment, determining which plants and animals were able to survive. The land mass could be a barrier as well as a bridge: during colder periods, glaciers advanced and precipitation levels dropped. During warmer intervals clouds, rain and snowaltered soils and drainage patterns. Fossilremains show that spruce, birchand poplars once grew beyond their northernmost modern range today, indicating there were periods when the climate was warmer and wetter. Mastodons, which depended on shrubs for food, were uncommon in the open dry tundralandscape characteristic of Beringia during the colder periods; in this tundra, mammoths flourished instead.
The Bering land bridge is significant for several reasons, not least because it is believed to have enabled
human migrationto the Americas from Asia about 25,000 years ago. [National Genographic. "Atlas of the Human Journey." 2005. May 2, 2007. [https://www3.nationalgeographic.com/genographic/atlas.html] ] A study by Hey (2005) [ cite journal | last = Hey | first = Jody | authorlink = | coauthors = | year = 2005 | month = | title = On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas | journal = PLoS Biology| volume = 3 | issue = 6 | pages = e193 | doi = 10.1371/journal.pbio.0030193 | url = | accessdate = | quote = ] have indicated that of the people migrating across this land bridge during that time period, only 70 left their genetic print in modern descendants, a minute effective founder population—easily misread as though implying that only 70 people crossed to North America. Seagoing coastal settlers may also have crossed much earlier, but scientific opinionremains divided on this point, and the coastal sites that would offer further information now lie submerged in up to a hundred metres of water offshore. Land animals were able to migrate through Beringia as well, bringing mammals that evolved in Asia to North America, mammals such as proboscideans and lions, which evolved into now-extinct endemic North American species, and allowing equids and camelids that evolved in North America (and later became extinct there) to migrate to Asia.
A new study published November 26, 2007 (see PLoS Genetics), which was led by University of Michigan and University College London researchers, seems to suggest that the Bering land bridge migration occurred during one specific time period which was 12,000 years ago, that every human who migrated across the land bridge all came from Eastern Siberia during that time period, and that every native American is directly descended from that same group of Eastern Siberian migrants. [ cite journal | last = Wang | first = Sijia | authorlink = | coauthors = Lewis, C. M. Jr.; Jakobsson, M.; Ramachandran, S.; Ray, N.; "et al." | year = 2007 | month = | title = Genetic Variation and Population Structure in Native Americans | journal =
PLoS Genetics| volume = 3 | issue = 11 | pages = e185 | doi = 10.1371/journal.pgen.0030185 | url = | accessdate = | quote = ] The claim suggests that a "unique genetic variant widespread in natives across both continents — suggesting that the first humans in the Americas came in a single migration or multiple waves from a single source, not in waves of migrations from different sources".
Biogeographical evidence demonstrates previous connections between North America and Asia. Similar
dinosaurfossils have been found between Asiaand North America. For instance the dinosaur " Saurolophus" was found in both Mongolia and western North America. Relatives of " Troodon", " Triceratops", and even "Tyrannosaurus rex" all came from Asia.
While there is considerable evidence for faunal interchange of dinosaurs in the Campanian and Maastrichtian phases of the Late Cretaceous, mammals, however, seem not to have dispersed so easily, perhaps because of their relatively small size; at any rate, there is no direct evidence supporting mammalian faunal exchange in the Cretaceous [Weil.] . Fossils in
Chinademonstrate a migration of Asian mammals into North America around 55 million years ago. By 20 million years ago, evidence in North America shows a further interchange of mammalian species. Some, like the ancient saber-toothed cats, have a recurring geographical range: Europe, Africa, Asia, and North America. The only way they could reach the New Worldis through the Bering land bridge. Had this bridge not existed at that time, the fauna of the world would be very different.
phylogeneticsis now being used to trace the history of faunal exchange and diversification, through the genetic history of parasites and pathogens of North American ungulates. An international Beringian Coevolution Project is collaborating to provide material to assess the pattern and timing of faunal exchange and the potential impact of past climatic events on differentiation.
* [http://www.nps.gov/bela/ Bering Land Bridge National Preserve]
* [http://www.beringstraitcrossing.com "The Bering Strait Crossing" by James A. Oliver ISBN 0954699564 Information Architects 2006 & 2007 (Revised)]
* [http://www.nps.gov/akso/beringia/whatisberingia2.htm What is Beringia?]
* [http://weber.ucsd.edu/~dkjordan/arch/beringia.html#top D.K. Jordan, "Prehistoric Beringia"]
* [http://www.ngdc.noaa.gov/paleo/parcs/atlas/beringia/lbridge.html Paleoenvironmental atlas of Beringia:] includes animation showing the gradual disappearance of the Bering land bridge
* [http://www.beringia.com/ Yukon Beringia Interpretive Centre]
* [http://www.geo.umass.edu/projects/chukotka/berhome.html Paleoenvironments and Glaciation in Beringia]
* [http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_41476.htm Anne Weil, 2002. "Late Cretaceous and early Paleocene mammalian exchange between Asia and North America"]
* [http://dsc.discovery.com/news/2008/02/13/beringia-native-american-02.html Study suggests 20000 year hiatus in Beringia]
* [http://download.ajhg.org/AJHG/pdf/PIIS0002929708001390.pdf 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 (3 March 2008). pdf file of article (525kb)
* Pielou, E. C., "After the Ice Age : The Return of Life to Glaciated North America" 1992
*Hey, Jody, 2005. "On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas" in "PLoS Biol" 2005 May 24;3(6):e193 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15898833&query_hl=1]
* Wisconsinan Stage
Geologic time scale
Bering Strait Bridge
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