According to the conventional theory, a migration corridor into North America became passable after the Cordilleran and Laurentide ice sheets receded.
Notes on verification
Confirmed by multiple independent, high-quality sources including peer-reviewed studies in Nature and PNAS, plus corroborating journalism. [tier=gold indep_score=0.983 clusters=3 claim_tier=notable]
Sources
- New Study Refutes Theory of How Humans Populated North America | HISTORY (seed:history_and_archaeology)
- https://www.nature.com/articles/nature19085 (corroboration)
- https://www.pnas.org/doi/10.1073/pnas.1601077113 (corroboration)
- https://www.cbc.ca/news/science/ice-free-corridor-north-americans-1.3715397 (corroboration)