Trails of footprints called “ghost tracks” have been seen in the White Sands area for years, but usually only when the ground was wet.NPS, USGS and Bournemouth University

The tracks at this site are both the oldest known footprints and the oldest solid proof of humans in North or South America, dating from 21,000 to 23,000 years ago — several thousand years earlier than what scientists previously thought.

“It’s the first irrefutable evidence for humans in the Americas,” says lead author Matthew Bennett of Bournemouth University in the U.K., about the tool.

Fossilized human footprints have been discovered in the east of the national park, where the bed of a “paleo-lake,” which is now dry, provides the gypsum-rich earth that is eroded by the wind to create the enormous white dunes for which the area is famous.

Because their foundations were based on what appeared to be stone tools that might have formed naturally, or on things that moved from their original stratigraphic layers, Bennett said, early human settlements had been disputed.