NATURE NOTES:
At White Sands, “Ghost Prints” Reveal the Antiquity of Human Life in the Americas

By Andrew Stuart

There are few recent archeological finds as awe-inspiring as the “ghost tracks” of White Sands National Park, near Alamogordo, New Mexico. These footprints, or trackways – which exist in the thousands, and become visible and then vanish, depending on moisture levels – capture the movements of mammoths, camels, dire wolves – and Ice-Age people. They bring small moments to life – of young people at play, of children being hoisted and set down by elders. And they record human encounters with great Ice-Age animals – like the group hunt of an elephant-sized ground sloth.

Now, they’ve yielded up something even more remarkable. On Sept. 23rd, an international team of scientists announced they’d dated tracks – to 23,000 years old. Those findings push back the date for human occupation of the continent by more than 8,000 years – and could fundamentally reshape our understanding of human history in the Americas. 

Dr. Jeffrey Pigati and Kathleen Springer are scientists with the U.S. Geological Survey. 

“And of course our first reaction was: ‘Holy mackerel – this is old,’” Pigati said.

“Those weren’t the exact words,” Springer said.

“Yeah – exactly,” Pigati said. “Thank you. That was the first thing – then the second thing was: We better make sure we’re right. If we’re going to push back the peopling of the Americas by many thousands of years, we better know exactly what we’re doing.”

The prints were first identified in 2006, by the park’s resource chief, David Bustos. Erosion exposes them at the surface – then, within a couple years, scours them away, and studies had focused on documenting surface prints before they were lost. 

But Springer and Pigati, who specialize in “paleo ecosystems,” knew they’d need to find tracks “in situ,” beneath the surface, for dating. Their colleague Thomas Urban used ground-penetrating radar to find buried prints, and the crew dug a trench.

Radiocarbon dating requires organic material. Above and below the buried prints, the scientists found seeds from Ruppia cirrhosa, a ditch grass that grows in shallow, standing water. 

Seeds, of course, can move around. To date the prints reliably, Pigati and Springer needed to confirm that seeds were in the spots where they’d grown, and they took great care in that area. Many of the seeds they dated were still attached to plant stems.

“So we know for a fact that they did not move around,” Pigati said. “These things are in completely the same place as when they were alive. One of the cool things – some of these people were walking across the landscape, and were stepping on the plants, and we actually pulled the seeds right out of the footprints, where they’d smushed them.”

The dates span a 2,000 year range, from between about 23,000 to 21,000 years ago. Those dates correspond with a warming period – when an expansive Ice-Age lake here receded, and people – and other creatures – could leave their footprints on its muddy margins.

The implications of the findings are vast. For a century, the archeological consensus has been that the oldest evidence of humans in the Americas was the Clovis culture, about 13,000 years ago. Potential “pre-Clovis” sites have been identified elsewhere – but nothing remotely this ancient.

The findings also indicate that people coexisted with Ice-Age “megafauna” for many thousands of years. That suggests that human hunting may not have been a prime factor in the extinction of those great animals.

The White Sands findings will be scrutinized and questioned. But scientists have greeted them as eminently credible. And they’ve been hailed as “probably the biggest discovery about the peopling of America in a hundred years.”

For Pigati and Springer, and the wider international team, the work is ongoing.

“Jeff and I are actually going to be in park for next three years,” Springer said, “doing various studies in line with what we’re talking about right now. Going to other parts of park, really performing the same type of exercise, the same methodologies, to really establish stratigraphies and chronologies that integrate the megafaunal and human trackways in a unifying framework. We’ll be busy now. We get to go out in the field again – it’s exciting.”

From the Clovis site to Lubbock Lake, the plains and deserts of New Mexico and West Texas have been central to our understanding of the first Americans. At White Sands, that legacy has extended – in a transformational way.