Land bridge

In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea levels fall, exposing shallow, previously submerged sections of continental shelf; or when new land is created by plate tectonics; or occasionally when the sea floor rises due to post-glacial rebound after an ice age.

The Isthmus of Panama is a land bridge whose appearance 3 million years ago enabled the Great American Biotic Interchange, in which animals and plants from the north colonized the south, and vice versa.[1]

Prominent examples

Map of Sahul and Sunda, land masses that have provided land bridges at various points throughout the Pleistocene

Former land bridges

The Bassian Plain, which linked Australia and Tasmania
The Bering Land Bridge (aka Beringia), which intermittently connected Alaska (Northern America) with Siberia (North Asia) as sea levels rose and fell under the effect of ice ages
Land bridges of Japan, several land bridges which connected Japan to Russia and Korea at various times in history.
De Geer Land Bridge, a route that connected Fennoscandia to northern Greenland
Doggerland, a former landmass in the southern North Sea which connected the island of Great Britain to continental Europe during the last ice age
The Thule Land Bridge, a since disappeared land bridge between the British Isles and Greenland
Torres Strait land bridge, Sahul, between modern-day West Papua and Cape York
Sundaland, a 1,800,000 km² area which connected the islands of Southeast Asia at various points during the last 2.6 million years

Current land bridges

Adam's Bridge (also known as Rama Setu), connecting India and Sri Lanka
The Isthmus of Panama, whose appearance three million years ago allowed the Great American Biotic Interchange between North America and South America[1]
The Sinai Peninsula, linking Africa and Eurasia

Land bridge theory

In the 19th century, scientists including Joseph Dalton Hooker noted puzzling geological, botanical, and zoological similarities between widely separated areas. To solve these problems, they proposed land bridges between appropriate land masses.[2][3] In geology, the concept was first proposed by Jules Marcou in Lettres sur les roches du Jura et leur distribution géographique dans les deux hémisphères ("Letters on the rocks of the Jura [Mountains] and their geographic distribution in the two hemispheres"), 1857–1860.[3]

The hypothetical land bridges included:[3]

Archatlantis from the West Indies to North Africa
Archhelenis from Brazil to South Africa
Archiboreis in the North Atlantic
Archigalenis from Central America through Hawaii to Northeast Asia
Archinotis from South America to Antarctica
Lemuria in the Indian Ocean

The theory of continental drift provided an alternate explanation that did not require land bridges. However the continental drift theory was not widely accepted until the development of plate tectonics in the early 1960s, which more completely explained the motion of continents over geological time.

References

Webb, S. David (23 August 2006). "The Great American Biotic Interchange: Patterns and Processes". Annals of the Missouri Botanical Garden. 93 (2): 245–257. doi:10.3417/0026-6493(2006)93[245:TGABIP]2.0.CO;2. S2CID 198152030.
Winkworth, Richard C. (2010). "Darwin and dispersal". Biology International. 47: 139–144.
Corliss, William R. (June 1975). Mysteries Beneath the Sea. Apollo Editions. ISBN 978-0815203735. Chapter 5: "Up-and-Down Landbridges".

External links

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[Webb_2006-1] Webb, S. David (23 August 2006). "The Great American Biotic Interchange: Patterns and Processes". Annals of the Missouri Botanical Garden. 93 (2): 245–257. doi:10.3417/0026-6493(2006)93[245:TGABIP]2.0.CO;2. S2CID 198152030.

[2] Winkworth, Richard C. (2010). "Darwin and dispersal". Biology International. 47: 139–144.

[corliss-3] Corliss, William R. (June 1975). Mysteries Beneath the Sea. Apollo Editions. ISBN 978-0815203735. Chapter 5: "Up-and-Down Landbridges".