Beringia, the Bering Land Bridge

During the ice ages so much water was locked in ice sheets that global sea level dropped, at the Last Glacial Maximum by about 120 metres. The shallow sea floor between Siberia and Alaska emerged, forming a landmass called Beringia up to about 1,600 kilometres wide from north to south. It was not an icy waste. Dry, cold air and little snow made it a grassland, the western end of the mammoth steppe, with mammoths, horses, bison, woolly rhinoceroses and saiga antelope, among others.

Because the land connection opened many times during the Pleistocene, animals crossed in both directions. Horses and camels, which evolved in North America, spread to Asia, while bison and mammoths came from Asia. Beringia also acted as a refuge for plants. Genetic evidence has led some researchers to propose a Beringian standstill, in which ancestors of Native Americans spent thousands of years there during the Last Glacial Maximum before spreading south. Rising seas flooded the bridge by about 11,000 years ago, and today the Bering Strait is about 85 kilometres wide, with the Diomede Islands in between.