The surviving footprints of a life that roamed millennia ago can be found in New Mexico on the wide expanse of an ancient lakebed.

Ancient footprints. Credit: James Allan, CC BY-SA 2.0

According to a study released in September 2021, these footprints are definitive evidence of human habitation of North America during the last ice age, which lasted between 23,000 and 21,000 years ago.

The footprints were discovered in an ancient lakebed with evidence of giant sloths and mammoths, and the study determined that they were the earliest unequivocal evidence of human occupation anywhere in the Americas during the Last Glacial Maximum.

Now, a new study disputes the evidence of such an early age. In Quaternary Research, scientists from DRI, Kansas State University, the University of Nevada, Reno, and Oregon State University say that the dating evidence is insufficient for claims that would fundamentally alter our understanding of when and how humans first arrived in North America.

Using the same dating technique and materials, the new study shows that the footprints could have been left thousands of years later than previously thought.

“I read the original Science article on the human footprints at White Sands and was initially struck, not only by how tremendous the footprints were on their own, but how important accurate dating would be,” said Charles Oviatt, emeritus professor of geology at Kansas State University and one of the study’s authors. “I detected potential flaws in the scientific tests of the dates reported in the Science paper.”

Paleogeneticists suggest that the American Southwest was first occupied no earlier than 20 thousand years ago, by studying ancient DNA from human fossils and using rates of genetic change (a kind of molecular clock using DNA). If the footprints are older, the use and integrity of these genetic models are called into question.

The tiny seeds used to date the footprints using radiocarbon dating methods, in which researchers analyze Carbon-14 that originates in the atmosphere and is absorbed by plants through pH๏τosynthesis, are at the center of the argument.

Scientists generally believe that the earliest known dates of human colonization of North America are between 14 and 16 thousand years ago, based on these methods. Current chronological models in fields as varied as paleogenetics and regional geochronology would need to be re-evaluated if the original claims are correct.

The authors write that it’s possible that the ages from a single study at a single site in a New Mexico lake basin are accurate and that age estimates from a variety of other fields are incorrect, but that more robust evidence is required to confirm the claims.

“It really calls a lot of what we thought we knew into question,” says David Rhode, Ph.D., a paleoecologist at DRI and study co-author. “That’s why it’s critical to really nail down this age, and why we’re arguing for more evidence.”

“These trackways really are a great resource for understanding the past, there’s no doubt about that. I’d love to see them myself. I’m just cautious about the ages that the researchers put to them,” he said.

More information: Oviatt, C., Madsen, D., Rhode, D., & Davis, L. (2022). A critical ᴀssessment of claims that human footprints in the Lake Otero basin, New Mexico date to the Last Glacial Maximum. Quaternary Research, 1-10. doi:10.1017/qua.2022.38