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Land bridges connect otherwise separated islands or continents, allowing for the exchange of plants and animals. The Bering land bridge, which allowed humans to migrate from Asia to the Americas, is the most famous. Other land bridges include Doggerland, which connected England to mainland Europe, and those in Indonesia. The land bridge between North and South America, formed by continental drift, exposed South America to flora and fauna from the rest of the world.
A land bridge is an isthmus or some other land connection between two otherwise disconnected islands or continents. Land bridges are ecologically important because they allow for the exchange of otherwise separated plants and/or animals, sometimes from millions of years of independent evolution. Land bridges are often transient, appearing and disappearing over geologic time due to rising and falling sea levels.
The most famous land bridge in Earth’s history is probably the Bering land bridge, which existed from present-day eastern Russia to Alaska about 20,000 years ago, during the last glacial period. During this period, sea levels were about 120 meters (394 feet) below today’s levels, due to massive amounts of ice locked up in continental glaciers. The Bering land bridge allowed humans to migrate from Asia to the Americas. After crossing, they are thought to have migrated along the coast.
Although the Bering land bridge is the most famous, there were many other land bridges in the world at one time. These include the large stretch of low-lying tundra in what is now the southern North Sea, which has been nicknamed Doggerland, after the Dogger Bank, a large sandbar in the area today. Doggerland connected England with mainland Europe and a separate land bridge connected England to Ireland. The first inhabitants of these islands crossed it by land bridges.
There were extensive land bridges between the islands in present-day Indonesia, connecting them to the Southeast Asian mainland. These allowed early humans to travel from Africa to islands like Borneo. In what is the first confirmed case of humans traveling over a significant stretch of open ocean, early humans built rafts and crossed what is now the Wallace Line, a deep-water channel in central Indonesia that separates Indonesia’s fauna western (which is more Asian) from eastern Indonesia (more Australian). From the east side of the Wallace Line, these people reached New Guinea and Australia, also connected by land bridges.
Further back in the past, about 2 million years ago, one of the most ecologically significant land bridges in the world was formed, the one between North and South America. Unlike the other land bridges discussed, this one was formed by continental drift rather than lower sea levels. Since South America had previously been isolated for tens of millions of years, this exposed the continent to flora and fauna essentially from the rest of the world (Europe, Africa, Asia and North America were all connected). In general, the North American fauna dominated the South American fauna, although some South American animals thrived in North America, for example the opossum.
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