The surviving footprints, found in New Mexico’s Lake Otero Basin, would revolutionize scientific understanding of how and when humans first arrived in North America if accurately dated. A new study challenges the age statement. – ScienceDaily

The expanse of an ancient lake bed in New Mexico contains the surviving traces of life that roamed millennia ago. Huge sloths and mammoths left their mark, and next to them marks of our human ancestors. Research published in September 2021 claimed these footprints were “definitive evidence of human occupation of North America” ​​during the last Ice Age, dating back 23,000 to 21,000 years ago. Now a new study disputes the evidence for such an early age.

Scientists from DRI, Kansas State University, the University of Nevada, Reno and Oregon State University are warning quaternary research that the dating evidence is insufficient for claims that would so radically alter our understanding of when and how humans first came to North America. Using the same dating method and materials, the new study shows the footprints may have been left thousands of years later than originally claimed.

“I read the original Science article on the human footprints at White Sands and was initially impressed not only by how massive the footprints themselves were, but also by the importance of accurate dating,” says Charles Oviatt, professor emeritus of geology at Kansas State University and one The new study’s authors: “I saw potential problems with the scientific testing of the data reported in the Science Paper.”

“It really challenges a lot of what we think we know,” says David Rhode, Ph.D., a paleoecologist at DRI and co-author of the new study. “That’s why it’s important to really nail that age, and that’s why we’re suggesting we need better evidence.”

Archaeologists and historians use a variety of methods to determine the timing of historical events. Based on these methods, scientists agree that the earliest known dates of human settlement in North America are 14,000 to 16,000 years ago after the last Ice Age. If the original claims are correct, current chronological models would need to be reevaluated in fields as diverse as paleogenetics and regional geochronology.

“Around 23,000 to 21,000 years ago, you really have to look at how people came to North America,” says Rhode. “Back then, Canada was covered in the north by a huge, kilometer-high mountain range of ice, and the path along the Pacific coast wasn’t very accommodating either — so maybe it had to be that people had to come here a lot earlier.”

By examining ancient DNA from human fossils and using rates of genetic change (a type of molecular clock that uses DNA), paleogeneticists theorize that the American Southwest was first settled no earlier than 20,000 years ago. If the footprints are older, this calls into question the use and integrity of these genetic models. It’s possible that the age from a study at a single site in a New Mexico lake basin is valid and that estimates of ages from a variety of other areas are invalid, the authors write, but more robust evidence is needed to support the claims.

At the heart of the debate are the tiny seeds of an aquatic plant that are used to age footprints. The time frame for the seeds was identified using radiocarbon dating methods, in which researchers study a type of carbon called carbon-14. Carbon-14 comes from the atmosphere and is taken up by plants through photosynthesis. These carbon isotopes decay at a constant rate over time, and comparing the amount of carbon-14 in the atmosphere with the amount in fossilized plant material allows scientists to determine their approximate age. But the plant species used Ruppia cirrhosagrows under water and therefore does not obtain a large part of its carbon for photosynthesis directly from the atmosphere like land plants, but from dissolved carbon atoms in the water.

“While the researchers recognize the problem, they underestimate the basic biology of the plant,” says Rhode. “For the most part, it uses the carbon it finds in lake water. And in most cases, that means it’s picking up carbon from sources other than today’s atmosphere — sources that are usually quite ancient.”

This method likely provides radiocarbon-based age estimates of the plant that are much older than the plants themselves. Ancient carbon enters the groundwater of the Lake Otero basin from the eroded bedrock of the Tularosa Valley and surrounding mountains and occurs in extensive calcium carbonate deposits throughout basin in front.

The authors have demonstrated this effect through investigations Ruppia Plant material of known age from the same region. Botanists collected living things Ruppia plants from a nearby spring pond in 1947 and archived them in the University of New Mexico Herbarium. Using the same radiocarbon dating method, the plants living in 1947 returned a radiocarbon date suggesting they were about 7400 years old, an offset resulting from the plant’s use of ancient groundwater. The authors note that when the age of Ruppia Seeds dated from human footprints have also been offset by about 7,400 years, their actual age would be between 15 and 13,000 years old – a date consistent with the age of several other known early North American archaeological sites.

Dating of the footprints can be solved by other methods, including radiocarbon dating of land plants (which use atmospheric carbon rather than carbon from groundwater) and optically stimulated luminescence dating of quartz found in the sediment, the authors write.

“These tracks really are a great resource for understanding the past, there’s no doubt about that,” says Rhode. “I’d like to see them myself. I’m just wary of the age that researchers give them.”