Land bridge

Image:Pm-map.png|thumb|upright=1.7|The Isthmus of Panama is a land bridge whose appearance 3 million years ago closed the Central American Seaway and enabled the Great American Biotic Interchange, in which animals and plants from the north colonized the south, and vice versa.
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.

Prominent examples

Image:Map of Sunda and Sahul.svg|300px|thumb|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 Mainland Australia to Tasmania
The Antarctic Land Bridge, which connected Antarctica, Australia, and South America during the Late Cretaceous and Early Paleogene
The Bering Land Bridge, which intermittently connected Alaska with Siberia as sea levels rose and fell under the effect of ice ages
GAARlandia, a hypothesized land bridge which potentially connected the Greater Antilles with South America during the late Eocene or early Oligocene
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 now-vanished 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, a very shallow series of shoals 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
The Sinai Peninsula, linking Africa and Eurasia

Land bridge theory

In the late 19th and early 20th centuries, vanished land bridges were an explanation for observed affinities of plants and animals in distant locations. Such scientists as Joseph Dalton Hooker noted puzzling geological, botanical, and zoological similarities between widely separated areas, and proposed land bridges between appropriate land masses that allowed species to spread between land masses. 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, 1857–1860.
Hypothesized land bridges included:Archatlantis from the West Indies to North Africa Archhelenis from Brazil to South AfricaArchiboreis in the North AtlanticArchigalenis from Central America through Hawaii to Northeast AsiaArchinotis from South America to AntarcticaLemuria 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.