From NBC News (hat tip: Funk Heritage Center):
David Bustos heard about the “ghost tracks” when he first went to White Sands National Park in New Mexico to work as a wildlife scientist in 2005. When the ground was wet enough at certain times of the year, the ghostly footprints would appear on the otherwise blank earth, only to disappear again when it dried out.
It wasn’t until over 10 years later, in 2016, that scientists confirmed that the ghost tracks had been made by real people — and it’s only now that some of the ancient footprints at White Sands have been dated as the earliest in North America.
“We’d been suspicious of the age for a while, and so now we finally have that it’s really exciting,” Bustos said. “One of the neat things is that you can see mammoth prints in the layers a meter or so above the human footprints, so that just helps to confirm the whole story.”
The footprints at White Sands were dated by examining the seeds of an aquatic plant that once thrived along the shores of the dried-up lake, Ruppia cirrhosa, commonly known as ditchgrass. According to research published Thursday in the journal Science and co-authored by Bustos, the ancient ditchgrass seeds were found in layers of hard earth both above and below the many human footprints at the site, and they were radiocarbon-dated to determine their age.
The tracks at one location have been revealed as both the earliest known footprints and the oldest firm evidence of humans anywhere in the Americas, showing that people lived there 21,000 to 23,000 years ago — several thousand years earlier than scientists once believed.
More at the link.