Most anthropologists today believe that the ancestors of all American Indians emigrated from northeastern Asia across the Bering land bridge during the Ice Age, between 12,000 and 60,000 years ago. Known as the Bering Strait theory, this idea is supported by geological and biological evidence. As water became locked up in the polar ice caps, sea levels dropped as much as 300 feet. The Bering Sea between Siberia and Alaska is no more than 180 feet deep and would have been dry land at those times. The land bridge, called Beringia, was open several times in the last 60,000 years. Biologically, American Indians are quite similar to the peoples of northeastern Asia. They share a number of physical similarities in teeth, skeletal features, coloration,
