The preserved footprints found in New Mexico’s Lake Otero Basin would upend scientific understanding of how, and when, humans first arrived in North America, if they are accurately dated. A new study brings the age claim into question. — ScienceDaily

A vast expanse of ancient lake in New Mexico holds preserved traces of life that existed thousands of years ago. Giant sloths and mammoths left their mark, and next to them, the marks of our human ancestors. A study published in September 2021 said that these steps are “clear evidence of human habitation in North America” ​​during the last ice age, which began between 23 and 21 years ago. Now, a new study contradicts the evidence of such a young age.

Scientists from DRI, Kansas State University, University of Nevada, Reno, and Oregon State University warn about Quaternary Research that the evidence of the time period is not enough for statements that could significantly change our understanding of when and how people first arrived in North America. Using the same dating method and tools, the new study shows that the footprints could have been left thousands of years later than originally thought.

“I read the first one Science “I’ve seen potential problems with scientific tests of the dates reported on the planet,” says Charles Oviatt, a professor of geology at Kansas State University. Science paper.”

“It really throws off a lot of things that 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 confirm this age, and why we suggest we need better evidence.”

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Archaeologists and historians use many methods to determine the time of historical events. Based on these trends, scientists tend to agree that the earliest known dates of human colonization in North America are between 14 and 16 thousand years ago, after the last ice age. If the first statements are correct, the latest chronology models in different fields like paleogenetics and regional geochronology will need to be re-evaluated.

“23,000 to 21,000 years ago is when you need to look at how people got into North America,” says Rhode. kilometers long covering Canada in the north, and the route down to the Pacific Coast was also very inhospitable – so people may have had to come here a lot. before that.”

By studying ancient DNA from human fossils and using rates of genetic change (a type of molecular clock that uses DNA), paleogeneticists estimate that the American Southwest began to be inhabited in the 20 thousand ago. If the footprints are old, it calls into question the use and reliability of these genetics. It is possible that ages from one study at one site in a New Mexico lake are correct, and that age estimates from different sites are incorrect, the authors write, but more evidence is needed. power to confirm the charges.

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At the center of this debate is the tiny seed of an aquatic plant that is used for aging footprints. The age of the seeds was determined using radiocarbon dating techniques, where researchers analyze a type of carbon known as Carbon-14. Carbon-14 comes from the atmosphere and is absorbed by plants through photosynthesis. These isotopes of carbon 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 -scientist to know their approximate age. But the types of plants used, Ruppia cirrhosait grows underwater and thus obtains most of its carbon for photosynthesis not directly from the atmosphere as terrestrial plants do, but from carbon atoms dissolved in water.

“Although researchers recognize the problem, they underestimate the basic biology of this plant,” Rhode says. And often, that means it’s taking carbon from sources other than the present-day atmosphere — sources that are often very old.”

This method may provide radiocarbon-based age estimates of plants that are much older than the plants themselves. Ancient carbon enters the groundwater of the Lake Otero Basin from the bedrock of the Tularosa Valley and surrounding mountains, and occurs in many calcium carbonate deposits throughout the basin.

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The authors demonstrated this effect by examining Rupee a plant of known age from the same place. Botanists collected living things Rupee plants from a nearby spring-fed pond in 1947 and deposited them in the University of New Mexico herbarium. Using the same radiocarbon dating method, plants that were still alive in 1947 returned a radiocarbon date indicating that they were about 7,400 years old, a reduction due to water use. long underground is this plant. The authors note that if the age of Rupee The human fossils were also erased by about 7400 years, their actual age would be between 15 and 13 thousand years — a date that matches the age of other places the most famous ancient North American.

Footprint identification can be addressed by other methods, including radiocarbon dating of terrestrial plants (which use atmospheric carbon rather than carbon from groundwater) and The formation of light quartz is found in sediments, the authors write.

“These trails are a great resource for understanding the past, there’s no doubt about that,” says Rhode. “I like to see them myself. I’m just careful about the age the researchers put them at.”

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