The first humans to reach the Americas emigrated across the Bering Straits between Alaska and Siberia during a time when the Ice Age had locked up so much of the world's water that the level of the sea was considerably lower than it is now, and North America and Asia formed a single land mass. No one is quite sure when that was, but it may have been between 20,000 and 40,000 years ago. At any rate, the Sibero-Americans, whom we call "Indians" since the Columbus and his immediate successors thought that they were in India, came to the Western Hemisphere as Palaeolithic hunters and gatherers, just as all other humans were Palaeolithic hunters and gatherers.
