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Fossil footprints show humans in North America more than 21,000 years ago. Pre the Icebridge era

Updated: Jul 29, 2022

The footprints, the earliest firm evidence for humans in the Americas, show that people must have arrived here before the last Ice Age. 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.

Ghost Tracks of White Sands Scientists are uncovering fossilized footprints in the New Mexico desert that show how humans and Ice Age animals shared the landscape

The discovery presented a rare opportunity—the scientists could radiocarbon date the seeds to derive an approximate age of the footprints. The results confirmed the presence of humans there between 23,000 and 21,000 years ago, at a time when much of modern-day North America was under ice. That discovery revived longstanding questions about how and when people first inhabited the continent. If the dates are correct, they would disprove a commonly held theory that humans arrived thousands of years later, toward the end of the Ice Age.

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