Paleohuman footprints dotting New Mexico’s White Sands National Park are 23,000 to 21,000 years old, making them the oldest fossilized tracks left by people in North America, according to a new study. However, not everyone agrees with the results.
The study, which used two dating techniques to verify the track’s age, is a response to criticism that a previous study published in 2021 by the same group used unreliable material to date the footprints. Now, the three results, the previous, controversial one and the two new findings from different dating techniques, point to the tracks being between 23,000 and 21,000 years old. This means they date from around the time of the Last Glacial Maximum (26,500 to 19,000 years ago), the coldest part of the last ice age.
The early age of the track is very important. Before, archaeologists thought that the people of Clovis – known for their sharp-edged blade-shaped stone points found in North American archaeological sites – were the first humans to enter the Americas about 13,000 years ago. Only in recent decades have archaeologists discovered solid evidence for pre-Clovis, or people who were in the Americas before 13,000 years ago, but many of these newly discovered sites had shaky evidence or were only a few thousand years old older than the Clovis. .
The White Sands Track is now the oldest site in North America with direct evidence of humans and significantly pushes back the date of arrival of the first Americans.
Related: How did humans first arrive in the Americas?
“When the first paper came out, many archaeologists reached out and said, ‘It was only a matter of time. We knew people were here before,” he said Jeffrey Pigatiwith whom he co-leads the study Kathleen Springer. Both are research geologists with the US Geological Survey at the Center for Geosciences and Environmental Change in Denver. “We now have solid evidence of people here during the last glacial maximum,” he said.
But in 2022, a group of archaeologists pointed out in a rebuttal than the radiocarbon dated material used in the first article: the seeds of the aquatic plant Ruppia cirrhosa – They were unreliable.
Scientists had found that the seeds had been incorporated into the footprints, providing organic remains that could be dated by examining the footprints. radioactive decay of its carbon-14. But “Scabies is a notorious misinformer of his time,” Loren Davis, an anthropology professor at Oregon State University who co-authored the rebuttal, told Live Science. Unlike other organisms that once lived that inhale carbon-14 from the atmosphere,”Scabies it prefers to take its carbon from the lake water, not the atmosphere. And in doing that, if you get old carbon into the groundwater, you’re going to have old age in plants that aren’t that old,” Davis said.
In rebuttal, Davis and his colleagues suggested that the White Sands group use optically stimulated luminescence (OSL) dating, a technique that estimates how long it has been since quartz or feldspar grains were last exposed. time to intense heat or sunlight.
So, for the new article, published on Thursday (October 5) in the magazine scienceresearchers did just that.
The team examined grains of quartz beneath the footprints with OSL dating. They found that the layers with the footprints were at least 21,500 years old.
The team also isolated and then radiocarbon dated three soil samples that each contained 75,000 conifer pollen grains from the same imprint layers as the Scabies then Confer plants get their carbon-14 from the atmosphere, meaning they don’t have the same drawbacks as Scabies. The ages of about 23,000 years ago matched those of the quartz seeds and grains. “If the seed ages and the pollen ages and the luminescence ages match, then it’s case closed,” Pigati said. “We can stop arguing about ages.”
Actually, not yet, Davis said.
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According to a map showing where the White Sands team took the OSL samples, “it’s clear that all three OSL ages come from sediments that are stratigraphically below the runway horizons,” Davis told Live Science in an email So it’s possible that the quartz grains were deposited first and the footprints were deposited on top of them at a later date, possibly between 19,800 and 16,200 years ago, as an OSL sample shows, he said.
“That’s why it’s critical that the authors continue their efforts to get the OSL age of the sediments that actually buried the footprints,” Davis said. He added that it’s possible the pollen samples moved through the layers of the site over time, meaning they could also be older than the footprints.
But others were impressed by the findings.
“I think it’s a very big contribution and a very compelling and detailed case,” Thomas Higham, an archaeological scientist and radiocarbon dating specialist at the University of Vienna who was not involved in the study. I disagreed with Davis’s view that more OSL data is needed. “Getting these samples is no easy feat,” Higham said, adding that the team took into account the underlying date layer and used a model to cluster the ages of the footprints above them.
The initial 2021 finding was “a groundbreaking result,” Higham told Live Science. “I think duplicating and reproducing these results is a hallmark of the scientific method.”
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