In 1975, a veterinary student came across a curious bone in south-central Chile, about 36 miles east of the Pacific. It proved to be that of a mastodon, and as archaeologists explored the discovery site, they found the remains of ancient hearths, a brazier pit, and a 20-foot tentlike structure made of wood and animal hides.

The site is estimated to be 12,500 years old. If that’s accurate, these people occupied Chile a full millennium before humans are generally thought to have colonized the Americas. Who were they?