Nautical chart of Bering Strait, site of former land bridge between Asia and North America

Shrinking of the Bering land bridge

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. A nautical chart is a graphic representation of a maritime area and adjacent Coastal regions The Bering Strait (Берингов пролив Beringov proliv) is a sea Strait between Cape Dezhnev, Russia, the easternmost point (169°43' A land bridge, in Biogeography, is an Isthmus or other land connection between otherwise separate areas which allows Animals and Plants Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent Siberia (Сиби́рь Sibir) is the name given to the vast region constituting almost all of Northern Asia and for the most part currently serving The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets 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. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. For the Australian television series see Rain Shadow (TV series. The Pacific Ocean is the largest of the Earth 's Oceanic divisions The grassland steppe including the land bridge and stretching for several hundred miles either side of it has been called Beringia. In physical Geography, a steppe ( German, from степь - "a flat and arid land" степ - /stɛp/ тал - tal дала - /dɑlɑ/ pronounced

It is believed that a small human population of at most a few thousand may have 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. The Last Glacial Maximum (LGM refers to the time of maximum extent of the Ice sheets during the last Glaciation (the Würm or Wisconsin glaciation) approximately There are several popular models of migration to the New World proposed by the anthropological community ^[1][2][3][4]

Geography

The Bering Strait, the Chukchi Sea to the north and the Bering Sea to the south, are all shallow seas (map, right). The Bering Strait (Берингов пролив Beringov proliv) is a sea Strait between Cape Dezhnev, Russia, the easternmost point (169°43' Chukchi Sea (Чуко́тское мо́ре is a Marginal sea of the Arctic Ocean. The Bering (or Imarpik) Sea is a body of water in the Pacific Ocean that comprises a deep water basin (the Aleutian Basin) which rises through 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. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets The Arctic is the Region around the Earth 's North Pole, opposite the Antarctic region around the South Pole. Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface 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 both to New Guinea and to Tasmania, the British Isles were an extension of continental Europe via the English Channel, and the dry basin of the South China Sea linked Sumatra, Java and Borneo to the Asian mainland. For a topic outline on this subject see List of basic Australia topics. New Guinea, located just north of Australia, is the world's second largest island, having become separated from the Australian mainland when the area now known Tasmania is an Australian island and state of the same name It is located south of the eastern side of the Continent, being separated from it by Bass The British Isles (Irish variously Na hOileáin Bhriotanacha, Oileáin Iarthair Eorpa, Éire agus an Bhreatain Mhór; Ellanyn Goaldagh Eileanan The South China Sea is a Marginal sea south of China. It is a part of the Pacific Ocean, encompassing an area from Singapore to the Sumatra (also spelled Sumatera) is the sixth largest island in the world (approximately 470000 km² and is the largest island entirely in Indonesia (two Java (Jawa is an Island of Indonesia and the site of its Capital city Jakarta. Borneo is the third largest island in the world and is located at the centre of Maritime Southeast Asia.

The rise and fall of global sea levels has exposed and submerged the land bridge in several periods of the Pleistocene. The Pleistocene ('plaɪstəsin is the epoch from 18 million to 10000 years BP covering the world's recent period The bridging land mass called "Beringia" is believed to have existed both in the glaciation that occurred before 35,000 BC and during the more recent period 22,000-7,000 years ago. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. By c. 4000 BC the coastlines had assumed approximately their present configurations.

Beringia constantly transformed its ecology as the changing climate affected the environment, determining which plants and animals were able to survive. Ecology (from Greek grc οἶκος oikos, "house(hold" and grc -λογία -logia) is the scientific study of 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 snow altered soils and drainage patterns. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Fossil remains show that spruce, birch and poplars once grew beyond their northernmost modern range today, indicating there were periods when the climate was warmer and wetter. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Spruce refers to Trees of the genus Picea, a genus of about 35 species of Coniferous Evergreen trees in the Family Pinaceae Birch is the name of any Tree of the genus Betula ( Bé-tu-la) in the family Betulaceae, closely related to the Populus is a genus of between 25–35 species of Flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. Mastodons, which depended on shrubs for food, were uncommon in the open dry tundra landscape characteristic of Beringia during the colder periods; in this tundra, mammoths flourished instead. Mastodons or Mastodonts (from Greek μαστός and οδούς, meaning " Nipple tooth" are members of the extinct In physical Geography, tundra is an area where the Tree growth is hindered by low temperatures and short growing seasons A mammoth is any Species of the Extinct Genus Mammuthus. These Proboscideans are members of the elephant family and

Human habitation

Main article: Models of migration to the New World

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. There are several popular models of migration to the New World proposed by the anthropological community Human migration denotes any movement by Humans from one locality to another sometimes over long distances or ^[5] A study by Hey (2005)^[6] 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. In Population genetics, the founder effect refers to the loss of genetic variation when a new colony is established by a very small number of individuals from a larger Sea-going coastal settlers may also have crossed much earlier, but scientific opinion remains 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. Scientific consensus is the collective judgement position and Opinion of the community of Scientists in a particular field of Science at a particular 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. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Proboscidea is an order containing only one family of living animals Elephantidae the Elephants with three living Species ( African Bush The American lion (Panthera leo atrox also known as the North American lion, American Cave lion,or Panthera is an Extinct eVolution is the third Album by eLDee, it was due to be released in 2008 Endemism is the Ecological state of being unique to a place Endemic species are not naturally found elsewhere Equidae is the family of horse-like animals which belong to the order Perissodactyla. Camelids are members of the biological family Camelidae, the only living family in the suborder Tylopoda.

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. ^[7] 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".

Previous connections

Biogeographical evidence demonstrates previous connections between North America and Asia. Biogeography is the study of the distribution of Biodiversity over Space and Time. Similar dinosaur fossils have been found between Asia and North America. For instance the dinosaur Saurolophus was found in both Mongolia and western North America. Saurolophus (sɔˈrɒləfəs meaning "reptile crest" is a Genus of large hadrosaurine duckbill that lived about 70 million Relatives of Troodon, Triceratops, and even Tyrannosaurus rex all came from Asia. Troodon (or Troödon in older sources is a Genus of relatively small Bird -like Dinosaur from the Late Cretaceous Triceratops (traɪˈsɛrətɒps is an extinct Genus of herbivorous ceratopsid Dinosaur which lived during the late Maastrichtian Tyrannosaurus ( or, meaning 'tyrant lizard' is a Genus of Theropod Dinosaur.

However, while there is considerable evidence for faunal interchange of dinosaurs in the Campanian and Maastrichtian phases of the Late Cretaceous, mammals 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^[8]. Fossils in China demonstrate a migration of Asian mammals into North America around 55 million years ago. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National 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 terms saber-toothed cat, sabertooth, and saber-toothed tiger describe numerous species mainly in the families Felidae (subfamily Machairodontinae The only way they could reach the New World is through the Bering land bridge. The New World is one of the names used for the non-Eurasian/non-African parts of the Earth specifically the Americas and Australia. Had this bridge not existed at that time, the fauna of the world would be very different.

Most recently, molecular phylogenetics is now being used to trace the history of faunal exchange and diversification, through the genetic history of parasites and pathogens of North American ungulates. Ungulates (meaning roughly "being Hoofed quot or "hoofed animal" are several groups of Mammals most of which use the tips of their toes usually 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.

References

External links

• Bering Land Bridge National Preserve
• "The Bering Strait Crossing" by James A. Oliver ISBN 0954699564 Information Architects 2006 & 2007 (Revised)
• What is Beringia?
• D.K. Jordan, "Prehistoric Beringia"
• Paleoenvironmental atlas of Beringia: includes animation showing the gradual disappearance of the Bering land bridge
• Yukon Beringia Interpretive Centre
• Paleoenvironments and Glaciation in Beringia
• Anne Weil, 2002. "Late Cretaceous and early Paleocene mammalian exchange between Asia and North America"
• Study suggests 20000 year hiatus in Beringia
• 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). The American Journal of Human Genetics is a leading Journal in the field of human Genetics. pdf file of article (525kb)

Further reading

• 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 [2]

See also

• Wisconsinan glaciation
• Pleistocene epoch
• Geologic time scale
• Bering Strait Bridge