Origins of Paleoindians - The Land Bridge

The Land Bridge

Further information: Beringia and Models of migration to the New World

The Last Glacial Maximum (LGM) of the Wurm/Wisconsin glacial period occurred approximately 20,000-18,000 years ago. Extremely cold weather resulted in the formation of vast ice sheets across the Earth's northernmost and southernmost latitudes. Glaciers also formed south of the 30th parallel in the Andean Mountains along the western coast of South America. As the ice sheets formed, sea levels dropped worldwide. When the Bering and Chukchi Seas had dropped some 400 feet lower than their present level, land beneath the Bering Strait was exposed. This is referred to as Beringia, an ancient Ice Age subcontinent that united the eastern and western hemispheres .

The Bering land bridge was a treeless, grassy tundra over 1000 miles wide. Broad temperature fluctuations produced below-freezing nighttime conditions. Permafrost kept the soil frozen year round except in the summer, when the first few inches of topsoil became waterlogged and spongy.

Several groups from Asia migrated across Beringia to enter and populate North America. The standard model includes Eurasian big-game hunters travelling across Siberia to Beringia. Other models include Southeast Asians using watercraft to skip along the Pacific Rim, arriving in the Americas via a coastal route.

After 18,000 years ago, the world began to warm up and the ice sheets began to melt, causing sea levels to rise. Massive flooding occurred from 15,000 to 13,000 years ago, when ice dams high in the mountains were breached. By 14,000 years ago, the land bridge lay submerged beneath the Bering Strait .