Final answer:
The first people to reach the Americas possibly did so through the Bering Land Bridge, following migratory mammals on foot from Siberia to Alaska during the last ice age, and then spread throughout the continents as the ice sheets melted.
Step-by-step explanation:
Those that crossed over through the Bering Land Bridge to reach the Americas possibly did so by following a route that connected northeast Siberia with what is now Alaska. The land bridge was exposed during the last ice age approximately 20,000 years ago due to lower sea levels from glacial ice formation. This theory suggests the first inhabitants of the Americas crossed this marshy land on foot in pursuit of migratory mammals.
As glaciers retreated, these peoples made their way into the Americas, through a corridor between two melting ice sheets. They spread into various regions such as the coastal northwest, the northeast, and southeast parts of the continental United States, then further into Mexico, Central America, and South America. By fifteen thousand years ago at the earliest, human populations reached as far as the southern tip of South America and were dispersed throughout the Western Hemisphere.