Beringia — the vast land connection between Siberia and Alaska that was exposed during periods of lower sea level caused by glacial water storage — was not a narrow land bridge.

At its maximum extent, it was a continent-sized landmass, perhaps as wide as the current United States is from north to south, covered with grassland and shrub vegetation that supported large mammal populations.

It was, in the most literal sense, a fourth major landmass connecting Asia and North America for thousands of years during the Ice Age.

The timing of the crossing from Asia into the Americas via Beringia has been the subject of sustained debate and increasingly sophisticated modeling.

The genetic evidence from living and ancient Native American populations provides powerful constraints on when the founding population separated from its Asian relatives and when it began to diverge into the distinct populations that eventually occupied different parts of the hemisphere.