NOEL KING, HOST:
To an untrained eye, White Sands National Park in New Mexico looks like a 227-square-mile sandbox. But the park's resource program manager, David Bustos, says not only does it have a thriving ecosystem but just below the surface, White Sands contains literal footprints of a past long gone.
DAVID BUSTOS: We found really incredible mammoth prints. And we found elongated prints that look, you know, possibly like they could be human.
A MARTINEZ, HOST:
It took years to confirm them because a lot of these prints were not always visible.
BUSTOS: Sort of come and go with soil moisture. So they might always be there. But they're below the surface.
MARTINEZ: There are acres of so-called ghost track clusters around the park.
KING: And each of these sets of footprints tells a different story. There are stories of kids playing, of people foraging for food and even hunting animals, like the giant ground sloth.
BUSTOS: You can see a person runs right up to the sloth, you know, chest to chest, almost standing on their tiptoes. And the sloth spins around. And there's claw marks on the ground. And then another person comes up from the other direction. And the first person that ran up to the sloth, he steps backwards. So you can see the heel just stepping really deeply.
MARTINEZ: These prints have been studied for years. But it was always difficult to estimate how old they were until now. Bustos is co-author of a new study that suggests humans might have been in North America thousands of years before we originally thought.
BUSTOS: The common date is around 13,000 years ago. And so that pushes it back quite a ways.
KING: After analyzing some of the footprints, scientists determined that human beings may have been in North America as early as 21,000 years ago.
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