CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Migration to the Americas. Diagram showing the three theories (arrowed) for when and how humans first arrived in the Americas. The central arrow shows migration from Asia along an ice-free corridor through Alaska and Canada 15,000 years ago. The arrow at left shows humans from Asia sailing along an ice-free region south of Alaska to reach the western coast of North America. The third arrow right) shows Europeans crossing the Atlantic, possibly some 20,000 years ago.
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