The leading theory about how early humans arrived on the American continents is:
2. THEY WALKED FROM ASIA TO NORTH AMERICA OVER A STRIP OF LAND THAT HAS SINCE BEEN COVERED BY THE OCEAN.
This theory is known as the Bering Land Bridge theory, which posits that during the last Ice Age, a land bridge connected Asia and North America through the Bering Strait, allowing early humans to migrate into the Americas.