I found an interesting article today about the origins of Native American and Siberian languages. Researchers have found links between the Yeniseian languages of Siberia and the Na-Dene languages of North America, and believe that these two groups share a common ancestor. Their findings also suggested that these languages might have developed in Beringia, the land between Siberia and Alsaka that was above water during the last ice age from about 35,000 years. Genetic studies suggest that the ancestors of Na-Dene speakers left Siberia some 25,000 years ago, but the first traces of people in the Americas date to 15,000 years ago, so it is thought that they lived in Beringia in the meantime, until the ice retreated sufficiently to allow them into Alaska. Some of the people of Beringia are thought to have migrated back to Siberia as well.
I just came across a programme about Beringia on the BBC World Service.