Fossil footprints help tell us how ancient people lived. But such physical impressions are hard to find.

“You get all of these footprints from different species in the same time period interacting, and you can’t see them all the time. And some of them, you can never see—with the eye, that is. But we can we can still detect them with geophysical sensors.”

Cornell University archaeologist Thomas Urban. He and colleagues used ground-penetrating radar (GPR) to detect invisible traces of footsteps in White Sands National Monument in New Mexico. Their GPR device goes back and forth over an area in a grid pattern, which ultimately creates a 2-D radargram. The technique detects subtle differences in ground density.

Speaking about one set of otherwise imperceptible animal’s footprints, he says:

“These were caused by compression of sediment beneath the animal’s track. And they relate to the weight and momentum of the animal.”

Twelve thousand years ago, the White Sands area was a large, muddy flat, which was covered with footprints from various species. Urban is excited about the stories so many footsteps suggest. For example, the researchers found no evidence of shoes or sandals. They did find human and animal tracks crossing each other—which suggests the prints were left during a hunt.

The findings are in the journal Scientific Reports. [Thomas M. Urban et al, 3-D radar imaging unlocks the untapped behavioral and biomechanical archive of Pleistocene ghost tracks]

“This sort of unique setting has recorded all of the daily movements of people. They are actually more than we even thought because there are always some that aren’t visible.”

These techniques could be applied to older sites all around the world, perhaps even to find dinosaur tracks that have been sitting quietly—waiting, at long last, to be found.

—Eliene Augenbraun

[The above text is a transcript of this podcast.]