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Land bridge
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'''Land bridge''' is essentially a historical term; it refers to dry land exposed during periods of low
sea level (see
regression), connecting what are now separate
continents or
islands. The best-known is the
Bering land bridge, which connected
North Asia and
Alaska during the last
ice age, enabling humans to migrate from
Eurasia to
the Americas by walking. Another land bridge connected
Great Britain to
Europe at around the same time. A historic land bridge surviving to the present day is the
Sinai, connecting
North Africa with
Southwest Asia; across this land bridge
hominids and
humans have migrated out of Africa. A land bridge does not have to be narrow enough to be called an
isthmus.
Occurrence
Land bridges generally occur on
continental shelf continental shelves: the
Bering Strait, where the Bering Land Bridge was during the last glaciation, is part of the edge of the
North American plate. For causes of sea level changes, see
Sea level change.
A land bridge that rose from the sea floor because of upthrust at the edge of a continental plate is
Central America. Where the
Cocos Plate, an oceanic
tectonic plate off the west coast of Central America is being
subduction subducted in a
convergent boundary under the North American Plate to the north and the
South American Plate to the south, first an
island arc, and then continuous dry land have been created. 12,000 years ago was when the first humans crossed over to North and South America
Tectonic Plates
Before
tectonic plate theory, it was believed that land bridges could explain the occurrence of species in separate continents. Many land bridges were thought up, criss-crossing large areas of ocean. They also apparently disappeared without a trace. Continental drift made this theory negatable.
*
Bering land bridge connected North Asia and Alaska.
*
Sinai Peninsula connects North Africa (
Egypt) and Southwest Asia.
*
Isthmus of Panama connects
North America (
Panama) and
South America (
Colombia).
* There was a land bridge between the
British Isles and the continental
Europe (
France).
* There were land bridges between
Japan (including
Okinawa),
Sakhalin Island,
Korean Peninsula, and
China. At the time, the
Yellow Sea was completely land, and the
Sea of Japan was a large lake.
* There was a land bridge between
Iberian Peninsula (
Spain) and
North Africa (
Morocco). The
Mediterranean Sea became a large lake and eventually dried up completely.
* There were land bridges between
Malay Peninsula and
Indonesia. The combined
subcontinent is called
Sundaland.
* There were land bridges between
New Guinea,
Australia, and
Tasmania. The combined continent is called
Sahul.
Other meanings
Air rights
The term land bridge sometimes refers to covering transportation facilities with bridges for non-transportation uses, such as parks, housing, or offices. For this use, see
air rights.
Containers on Railways
In the
railroad industry, '''land bridge''' refers to the transport of
containerization containers by rail between
ports on either side of a land mass, such as
North America.
Saudi Arabia
In 2005
Transportation in Saudi Arabia Saudi Arabia initiated a 3,000 km project of railway construction to link cities, ports and mines within the country, and potentially with adjacent countries.
Wildlife
The term '''land bridge''' is sometimes used for wide bridges built over highways for wildlife and park users to cross. A natural crossing of a waterway is known as a
natural arch or natural bridge.
External links
-
Florida DEP - Cross Florida Greenway Land Bridge
Category:Geology
it:Ponte continentale
pt:Beríngia
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