Footprints left by prehistoric humans may be some of the strongest evidence that humans arrived in the Americas earlier than previously thought.
More than 60 “ghost tracks” — so-called because they appear and disappear across the landscape — show that people walked what is now New Mexico between 23,000 and 21,000 years ago, geophysicist Matthew Bennett and colleagues report in Science 24 September . If true, the fossil findings would be the definitive proof that humans were in North America during the height of the last ice age, which peaked around 21,500 years ago.
When people first arrived in America is highly controversial. Scientists have historically believed that humans traveled across the Bering Land Bridge that connected Asia to North America around 13,000 years ago, after the vast Laurentian Ice Sheet, which once covered most of North America, began to retreat into the Arctic. But a number of recent discoveries from across North and South America, including some 30,000-year-old animal bones from a Mexican cave and stone tools from Texas, suggest that humans may have arrived much earlier.
At White Sands National Park in New Mexico, Bennett of Bournemouth University in Poole, England, and colleagues used several methods to calculate the age of the newly described tracks, including radiocarbon dating of aquatic plants embedded in and between the tracks.
“One of the great things about footprints is that, unlike stone tools or bones, they can’t be moved up or down the stratigraphy,” he says. “They’re fixed, and they’re very accurate.”
But some archaeologists are still not sure of the age of the traces. Lauren Davis, an anthropologist at Oregon State University in Corvallis, says he wishes researchers would use other verification methods to verify the dates before “breaking out the champagne.”
“That’s what makes you rewrite textbooks,” Davis says. “For the good of the industry, we need really high standards.” But if further testing confirms the age of the tracks, he says the discovery “will show us that humans have this amazing ability to survive and thrive at a time when global conditions were extreme.”
Researchers say the tracks were created over two millennia, mostly by children and teenagers who wandered the patchwork of waterways that defined the White Sands area during the Ice Age. These footprints were found alongside those of mammoths, giant ground sloths, and other megafauna that flocked to water in the mostly arid landscape.
Bennett plans to return to White Sands after the pandemic to continue studying the human footprints, hoping to learn more about the people who made them. “The tracks are like nothing else,” he says. “It’s very powerful to put your finger in the base of a track and know that someone walked that path 23,000 years ago.”