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Encyclopedic overview
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.
Excerpted from Wikipedia’s “land bridge” article, available under the CC BY-SA 4.0 licence.