A land bridge, in biogeography

Biogeography

Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

, is an isthmus

Isthmus

An isthmus is a narrow strip of land connecting two larger land areas usually with waterforms on either side.Canals are often built through isthmuses where they may be particularly advantageous to create a shortcut for marine transportation...

 or wider land connection between otherwise separate areas, over which animals and plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s are able to cross and colonise new lands. Land bridges can be created by marine regression

Marine regression

Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....

, in which sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

s fall, exposing shallow, previously submerged sections of continental shelf

Continental shelf

The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

; or when new land is created by plate tectonics

Plate tectonics

Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

; or occasionally when the sea floor rises due to post-glacial rebound

Post-glacial rebound

Post-glacial rebound is the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy...

 after an ice age

Ice age

An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

.

Prominent examples

• The Bering land bridge, which intermittently connected Asia with North America as sea levels rose and fell under the effect of ice ages;
• Doggerland
  Doggerland
  Doggerland is a name given by archaeologists and geologists to a former landmass in the southern North Sea that connected the island of Great Britain to mainland Europe during and after the last Ice Age, surviving until about 6,500 or 6,200 BCE, though gradually being swallowed by rising sea levels...
  
  , a former landmass in the southern North Sea
  North Sea
  In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
  
   which connected the island of Great Britain
  Great Britain
  Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
  
   to mainland Europe
  Europe
  Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
  
   during the last ice age.
• The Isthmus of Panama
  Isthmus of Panama
  The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal...
  
  , whose appearance 3 mya allowed the Great American Interchange
  Great American Interchange
  The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
  
  ;
• The Sinai Peninsula
  Sinai Peninsula
  The Sinai Peninsula or Sinai is a triangular peninsula in Egypt about in area. It is situated between the Mediterranean Sea to the north, and the Red Sea to the south, and is the only part of Egyptian territory located in Asia as opposed to Africa, effectively serving as a land bridge between two...
  
  , linking Africa
  Africa
  Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
  
   and Eurasia
  Eurasia
  Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
  
  ;

Land bridge theory

In the 19th century a number of scientists noted puzzling geological and zoological similarities between widely separated areas. To solve these problems, "…whenever geologists and paleontologists were at a loss to explain the obvious transoceanic similarities of life that they deduced from the fossil records, they sharpened their pencils and sketched land bridges between appropriate continents." The concept was first proposed by Jules Marcou

Jules Marcou

Jules Marcou was an eminent Swiss-American geologist.He was born at Salins, in the département of Jura, in France....

 in Lettres sur les roches du Jura.

These hypothetical land bridges included:

• 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
  Lemuria (continent)
  Lemuria is the name of a hypothetical "lost land" variously located in the Indian and Pacific Oceans. The concept's 19th century origins lie in attempts to account for discontinuities in biogeography; however, the concept of Lemuria has been rendered obsolete by modern theories of plate tectonics...
  
  in the Indian Ocean

All of these became obsolete with the gradual acceptance of continental drift

Continental drift

Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...

 and the development of plate tectonics

Plate tectonics

Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...

by the mid-20th century.