A physical land bridge, in biogeography, is an isthmus or other land connection between what at other times are separate land masses which allows animals and plants to cross and colonize new lands. Land bridges are commonly created by regression, in which sea levels fall exposing previously submerged sections of continental shelf. Land bridges are also formed by upthrust at the edge of continental plates.
The most recent significantly low sea levels were about 20,000 years ago (during the Upper Paleolithic) when worldwide sea levels were about 120 meters below today's level. By 10,000 years ago, the sea level had risen to 20 meters below today's level.
The best-known example is the Bering land bridge, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages, enabling humans to migrate from Eurasia to the Americas. Another land bridge may have connected Great Britain to Europe at around the same time.
A land bridge surviving to the present day is the Sinai, connecting North Africa with Southwest Asia. Hominids and humans probably migrated out of Africa through the Sinai.
A land bridge that rose from the sea floor because of upthrust at the edge of a continental plate is Central America. The Cocos Plate, an oceanic tectonic plate off the west coast of Central America, is being subducted in a convergent boundary under the North American Plate to the north and the South American Plate to the south. This caused first an island arc and then continuous land to emerge.
Before the theory of Plate Tectonics, it was believed that land bridges could explain the occurrence of species in separate continents. Many land bridges were thought up, cross-crossing large areas of ocean. They also apparently disappeared without a trace. Continental drift
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