How were the first Americans able to migrate to the western hemisphere 20000 or more years ago?

Answer 1

Fossil records and geological excavations indicate that a land bridge may have existed across the Bering Straits (now Alaska), long after the continents of Asia and North America were physically separated. Other investigations suggest that some Polynesians may have migrated across the South Pacific as well.

Answer 2

The first Americans are believed to have migrated to the Western Hemisphere from Asia via a land bridge known as Beringia, which existed during the last Ice Age. This land bridge connected Siberia and Alaska, allowing early humans to cross into North America. As the Ice Age ended, sea levels rose and the land bridge disappeared, isolating the populations in the Americas.