Traditional theories suggest big-animal hunters crossed the Bering Strait from North Asia into America over a land and ice bridge (Beringia). This bridge existed between 45,000–12,000 BCE (47,000–14,000 BP). Small isolated groups of hunter-gatherers migrated alongside herds of large herbivores far into Alaska. From c. 16,500 – c. 13,500 BCE (c. 18,500 – c. 15,500 BP), ice-free corridors developed along the Pacific coast and valleys of North America. This allowed animals, followed by humans, to migrate south into the interior. The people went on foot or used primitive boats along the coastline. The precise dates and routes of the peopling of the New World are subject to ongoing debate.
Stone tools, particularly projectile points and scrapers, are the primary evidence of the earliest human activity in the Americas. Crafted lithic flaked tools are used by archaeologists and anthropologists to classify cultural periods. Scientific evidence links Indigenous Americans to eastern Siberian populations. Indigenous peoples of the Americas have been linked to Siberian populations by linguistic factors, the distribution of blood types, and in genetic composition as reflected by molecular data, such as DNA. There is evidence for at least two separate migrations. Between 8000–7000 BCE (10,000–9,000 BP) the climate stabilized, leading to a rise in population and lithic technology advances, resulting in more sedentary lifestyle.
The specifics of Paleo-Indian migration to and throughout the Americas, including the exact dates and routes traveled, are subject to ongoing research and discussion. The traditional theory has been that these early migrants moved into Beringia between eastern Siberia and present-day Alaska 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.
Archaeologists contend that Paleo-Indians migration out of Beringia (western Alaska), ranges from c. 40,000 – c. 16,500 years ago. This time range is a source of debate and promises to continue as such for years to come. The few agreements achieved to date are the origin from Central Asia, with widespread habitation of the Americas during the end of the last glacial period, or more specifically what is known as the late glacial maximum, around 16,000–13,000 years before present. However, alternative theories about the origins of Paleoindians exist, including migration from Europe.
Sites in Alaska (East Beringia) are where some of the earliest evidence has been found of Paleo-Indians, followed by archaeological sites in northern British Columbia, western Alberta and the Old Crow Flats region in the Yukon. The Paleo-Indian would eventually flourish all over the Americas. These peoples were spread over a wide geographical area; thus there were regional variations in lifestyles. However, all the individual groups shared a common style of stone tool production, making knapping styles and progress identifiable. This early Paleo-Indian period lithic reduction tool adaptations have been found across the Americas, utilized by highly mobile bands consisting of approximately 20 to 60 members of an extended family. Food would have been plentiful during the few warm months of the year. Lakes and rivers were teeming with many species of fish, birds and aquatic mammals. Nuts, berries and edible roots could be found in the forests and marshes. The fall would have been a busy time because foodstuffs would have to be stored and clothing made ready for the winter. During the winter, coastal fishing groups moved inland to hunt and trap fresh food and furs.