An isthmus ( / ˈ ɪ s m ə s , ˈ ɪ s θ m ə s / ; pl. : isthmuses or isthmi ) is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar , and a strait is the sea counterpart of an isthmus, a narrow stretch of sea between two landmasses that connects two larger bodies of water.
5-428: Isthmus and land bridge are related terms, with isthmus having a broader meaning. A land bridge is an isthmus connecting Earth's major land masses. The term land bridge is usually used in biogeology to describe land connections that used to exist between continents at various times and were important for the migration of people and various species of animals and plants, e.g. Beringia and Doggerland . An isthmus
10-454: A particularly advantageous shortcut for marine transport. For example: 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
15-680: Is a land connection between two bigger landmasses, while a peninsula is rather a land protrusion that is connected to a bigger landmass on one side only and surrounded by water on all other sides. Technically, an isthmus can have canals running from coast to coast (e.g. the Panama Canal ), and thus resemble two peninsulas; however, canals are artificial features distinguished from straits . The world's major isthmuses include: Of historic importance were: The cities of Auckland , Madison , Manila , and Seattle are located on isthmuses. Canals are often built across isthmuses, where they may be
20-540: Is created by plate tectonics ; or occasionally when the sea floor rises due to post-glacial rebound after an ice age . In the late 19th and early 20 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,
25-524: 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. Hypothesized land bridges included: The theory of continental drift provided an alternate explanation that did not require land bridges. However
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