The Inuit and related peoples arrived separately and at a much later date, probably during the first millennium AD, moving across the ice from Siberia into Alaska.After the migration or migrations, it was several thousand years before the first complex civilizations arose, at the earliest emerging 5000 BCE.Genetic evidence found in Amerindians' maternally inherited mitochondrial DNA (mt DNA) supports the theory of multiple genetic populations migrating from Asia.Over the course of millennia, Paleo-Indians spread throughout North America and South America.
Over the course of thousands of years, American indigenous peoples domesticated, bred and cultivated a large array of plant species.
Within this timeframe, roughly pertaining to the Paleo-Indian Period, the Archaic Period, the Early Woodland Period, the Middle Woodland Period and the Late Woodland Period, numerous archaeological cultures have been identified.
Early Paleoamericans soon spread throughout the Americas, diversifying into many hundreds of culturally distinct nations and tribes.
The second belief is the long chronology theory, which proposes that the first group of people entered the hemisphere at a much earlier date, possibly 50,000 - 40,000 years ago or earlier.
Artifacts have been found in both North and South America which have been dated to 14,000 BP, and humans are thought to have reached Cape Horn at the southern tip of South America by this time.
late 15th–early 16th centuries), and are known only through archaeological investigations.