Humans
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Previous dating of the Monte Verde archaeological site drastically overestimated its age, perhaps by more than three times, a paper claims. The site has such an important place in the debate about the arrival of humans in the Americas – particularly South America – that the new estimate could create ripples across two continents, if the claim stands up to scrutiny.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.For a long time most archaeologists shared a view on how humans came to populate the Americas. As the last Ice Age was ending, went the story, a small group of people crossed a landbridge that is now the Bering Strait and through an ice-free corridor. They brought with them a style of stone-work known as the Clovis culture toolkit, identified by fluted projectile points found widely across North America around 13,000 years ago.
At some point, the story continued, the Clovis culture diversified, and practitioners of some of its replacements moved on to South America and the Caribbean. More recently, however, this account has come under attack from a great many angles, leaving few remaining supporters. One of the most significant contributors to the fall of “Clovis First” was the discovery of the site known as Monte Verde in southern Chile.
Monte Verde has stone tools, along with animal hides and even the remnants of rope, which in 1997 were dated as being 14,500 years old. If correct, this would either mean that humans arrived in South America before North America, overturning everything we thought we knew about humanity’s greatest migration, or that North America was populated well before Clovis. More recently, reported evidence for earlier arrival started coming thick and fast. A newer study added a further 3,500 years to the age of a subsample of the Monte Verde tools, but this has been less widely accepted than the original work.
However, a team led by Professor Todd Surovell of the University of Wyoming claims in a new study that the true age of the Monte Verde artifacts is actually 4,200-8,200 years ago, giving plenty of time for the Clovis makers to move south.
“Because of a validation of the Monte Verde site by outside experts 29 years ago, our understanding of the date of human arrival to the Americas was fundamentally changed,” Surovell said in a statement. “We now correct the record and show that the site is much younger than initially believed. With colonization of the Americas no longer anchored by Monte Verde, our revised chronology supports a more recent date of human arrival to the Americas.”
The paper has sparked a firestorm of discussion in archaeology-focused online chats. Naturally, some want time to check Surovell and colleagues’ work, in case the original date was right all along, pointing to evidence the new work has not addressed, such as the apparent presence of Ice Age species at the site. Others take the view that while Monte Verde created the first big challenge to "Clovis First", so many other old sites have been found since that its importance has waned. Meanwhile, another group is asking if one site can be so badly misdated, how much trust should be placed in estimates for others?
Surovell thinks textbooks need to be rewritten, although perhaps those from the early 1990s can be dug out of storage. “Monte Verde is best known as the site that broke the Clovis barrier, after a site visit in 1997 by external scholars who confirmed the archaeological nature and age of the site,” he said. “Findings from Monte Verde were so important that they were viewed as paradigm-changing, effectively rewriting the history of the last instances in which humans colonized previously uninhabited continental land masses.”
The first artifacts were found at Monte Verde in 1975, and since then, only the team that made the original discovery has participated in dating the site, until this new work. Surovell and colleagues argue that the previous dating failed to account for erosion along the Chinchihuapi Creek, on whose banks the site lies.
Wood from Ice Age trees became mixed with younger soil in which the artifacts were buried, Surovall’s team claims, and the carbon-14 ratios reflect this, distorting the original estimates. The team measured the age of three wood samples in one part of the site and got ages of more than 16,000 years – easily enough to distort the results from the surrounding soil if some wood broke down.
Such contamination could make it very difficult to get any accurate date for the site, were it not for a stroke of luck. Around 11,000 years ago, a volcanic eruption deposited ash widely across north-western Patagonia. Some of this ash has been found below the artifacts, not above them, as would be expected if the original age was correct. Although the authors cannot be very precise about the artifacts’ ages, several lines of evidence point to them being thousands of years younger than the ash.
Surovell and colleagues have already challenged the dating on some other sites that have been taken as further evidence for humans in North America long before Clovis. However, this is the first time they have looked at a South American site.
Meanwhile, footprints (and lines attributed to handcarts) in New Mexico have been dated to at least 21,000 years old, and were not among those Surovell has redated.
The study is open access in Science.
