Bering land bridge
The Bering land bridge, also known as Beringia, was a land bridge roughly 1,000 miles north to south at its greatest extent, which joined present-day
Alaska and eastern
Siberia at various times during the
Pleistocene ice ages. Beringia 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
Bering Strait, the
Chukchi Sea to the north and the
Bering Sea to the south, are all shallow seas . 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.
Encyclopedia
The
Bering land bridge, also known as
Beringia, was a land bridge roughly 1,000 miles north to south at its greatest extent, which joined present-day
Alaska and eastern
Siberia at various times during the
Pleistocene ice ages. Beringia 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
Bering Strait, the
Chukchi Sea to the north and the
Bering Sea to the south, are all shallow seas . 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. 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.
The Bering Land Bridge is significant for several reasons, not least because it enabled
human migration to the Americas from Asia about 12,000 years ago . Recent studies have indicated that of the people migrating across this land bridge during that time period, only 70 left their genetic print in modern descendents, a minute effective founder population— easily misread as though implying that only 70 people crossed to North America. 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. Land animals were able to migrate through Beringia as well, bringing mammals that evolved in Asia to
North America, mammals such as
lions and
cheetahs, which
evolved into now-extinct endemic North American species, and exporting
camelids that evolved in North America to Asia.
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 glaciation that 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
ecology as 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
snow altered
soils and drainage patterns.
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.
Mastodons, that 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.
Previous connections
Biogeographical evidence demonstrate previous connections between North America and Asia. 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. Relatives of
Troodon was a relatively small, bird [i]-like dinosaur [i] from the Late Cretaceous [i] Period [i] ...
,
Triceratops, and even
Tyrannosaurus rex is a genus [i] of tyrannosaurid [i] theropod [i] dinosaur [i]. ...
all came from Asia. Fossils in
China demonstrate 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 World is through the Bering land bridge. Had this bridge not existed at that time, the fauna of the world would be very different.
External links
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- includes animation showing the gradual disappearance of the Bering land bridge
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References
- 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:e193
See also
The
geological time scale is used by geologist [i]s and other scientists to describe the timing and ...
