Final answer:
The earliest Americans are believed to have come from northeastern Siberia, migrating via the Bering Land Bridge and coastal routes more than 20,000 years ago, as supported by genetic evidence.
Step-by-step explanation:
Archaeologists believe that the earliest Americans originated from northeastern Siberia and migrated to the Americas via the Bering Land Bridge or along coastal routes. The theory of the land bridge suggests that during the last ice age, sea levels were lower, exposing a land passage between Asia and North America. This allowed the Clovis culture, characterized by distinctive projectile points, to migrate into the Americas between 12,000-11,000 BCE. The coastal migration theory posits a journey along the shorelines by watercraft. Scientific evidence supports both of these routes, with genetic studies indicating that these first peoples migrated from Asia more than 20,000 years ago, contradicting more controversial hypotheses such as the Solutrean hypothesis suggesting European origins.