The history of North America is the study of the past, particularly the written record, oral histories, and traditions, passed down from generation to generation on the continent in the Earth's northern hemisphere and (chiefly) western hemisphere.
The specifics of Paleo-Indians migration to and throughout the Americas, including the exact dates and routes traveled, are subject to ongoing research and discussion. For years, the traditional theory has been that these early migrants moved into the Beringia land bridge between eastern Siberia and present-day Alaska around 40,000 â€” 17,000 years ago, when sea levels were significantly lowered due to the Quaternary glaciation. These people are believed to have followed herds of now-extinct pleistocene megafauna along ice-free corridors that stretched between the Laurentide and Cordilleran ice sheets.
Another route proposed is that, either on foot or using primitive boats, they migrated down the Pacific coast to South America. Evidence of the latter would since have been covered by a sea level rise of hundreds of meters following the last ice age.