NEW YORK – For decades, the strongest evidence for the earliest human settlement in the Americas came from a site in Chile called Monte Verde.
Scientists found echoes of human presence dating back to around 14,500 years ago, including footprints, wooden tools, foundations for a building and the remains of an ancient fire pit. They dated sediments and artifacts from the site to this time frame.
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A new study challenges the age of this important site, suggesting Monte Verde might be much younger than scientists thought. But not everyone agrees with the findings.
Scientists sampled and dated sediments from nine areas along the Chinchihuapi Creek by the site and analyzed how the landscape changed over thousands of years. They uncovered a layer of volcanic ash from an eruption dating back to about 11,000 years ago.
Anything above that layer — in this case, the Monte Verde wood and artifacts — had to be younger, according to study co-author Claudio Latorre.
“We basically reinterpreted the geology of the site. And we came to the conclusion that the Monte Verde site cannot be older than 8,200 years before present," said Latorre, who works at the Pontifical Catholic University of Chile.
The researchers think changes to the landscape, including a stream wearing down the rocks, may have mixed old layers with new, causing researchers to date ancient wood as part of the Monte Verde site.
The findings were published Thursday in the journal Science. Several scientists, including those involved with the original excavations, take issue with the results.
“They have provided, at best, a working hypothesis that is not supported by the data they presented,” said Michael Waters of Texas A&M University, who had no role in either study.
Experts not involved with the research say the study includes analysis of samples from the area surrounding Monte Verde, where the geology isn’t comparable to the site itself. And they say there's not enough evidence that the layer of volcanic ash once covered the entire landscape.
They also say the study doesn’t offer a sufficient explanation for the artifacts found at the site that have been directly dated to 14,500 years ago, including a mastodon tusk fashioned into a tool, a wooden lance and a digging stick with a burned tip.
“This interpretation disregards a vast body of well-dated cultural evidence,” archaeologist Tom Dillehay of Vanderbilt University, who led the site's first excavation, said in an email.
The new study's authors disagree with these criticisms, saying they sampled within, upstream and downstream of the site. And there's not enough evidence that the dated artifacts at the site really are that old, said co-author Todd Surovell, of the University of Wyoming.
The Monte Verde site is critical to scientists' understanding of how people got to the Americas. Scientists used to think the first arrivals were a group of people 13,000 years ago who made tipped stone tools known as Clovis points. The discovery and dating of Monte Verde, which was initially mired in controversy, appeared to put that to rest.
It's unclear how a new date for the site might affect the human story. Since Monte Verde, researchers have uncovered sites in North America that predate the Clovis people, such as Cooper’s Ferry in Idaho and the Debra L. Friedkin site in Texas.
But another big question is how, exactly, people got to the Americas from Asia, maneuvering south of two massive ice sheets covering Canada. Did humans arrive in time for the sheets to part, revealing an ice-free corridor? Did they travel along the coast in boats, or over a mix of water and land?
A revised date for Monte Verde could reopen discussions about the most likely route by early humans, said Surovell. Future independent analyses of other early human sites could provide more clarity.
“Given enough time and given the ability to do science, science is self-corrective," Surovell said. "It eventually reaches the truth.”
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