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In every scientific field, there are totemic places. The CERN physics laboratory that houses the Large Hadron Collider; the Cavendish lab in Cambridge where James Watson and Francis Crick did their research on the structure of DNA; NASA’s Jet Propulsion Laboratory in California.
In archaeology, one such place is a site in Chile called Monte Verde. For half a century, Monte Verde has been central to our understanding of the peopling of the Americas. For two decades, the story that Monte Verde told was wildly controversial. It then became fairly settled, but, as of this year, it has become controversial again.
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The details of the new argument are, at times, punishingly technical, and I’m going to give only the roughest outline of them or we’d be here all week. However, the actual questions at the back of all this are simple: who were the first people to live in the Americas, and when did they arrive?
The Americas were the last continents to be settled by humans. (Well, there’s Antarctica, but given it was discovered only within the last 300 years, let’s not worry about it.) The oldest known hominins lived in Africa, and we don’t see hard evidence of hominins anywhere else until 1.8 million years ago, when Homo erectus reached what is now Georgia – the one in Eurasia, not the US state. Later, hominins like Neanderthals and Denisovans spread throughout Eurasia. Later still, our species, Homo sapiens, appeared in Africa and migrated all over Eurasia.
That’s a lot of travelling around, over a period of nearly 2 million years. Yet none of those people seem to have reached the Americas. While the exact timing of that momentous landfall is very contentious, we are talking at most about the last 35,000 years – and the main waves of settlement seem to have been between 20,000 and 13,000 years ago.
That’s where Monte Verde comes in. It has long been claimed to be the oldest evidence of humans in the Americas – or at least the oldest one with indisputable traces of human intervention and reliable dating evidence. Monte Verde told us that people entered the Americas thousands of years earlier than previously thought.
Now, the archaeological data at the site is under attack – and with it, our understanding of the prehistory of the Americas.
Early Americans
Monte Verde is in southern Chile, a few tens of kilometres inland from the Pacific Ocean. To the south, the coast of South America fractures into a confusing scatter of peninsulas and islands. The Andes mountain chain, which runs north-south, lies to the east. Monte Verde sits on a flood plain: it is on the banks of the Chinchihuapi creek, a tributary of the larger MaullĂn river.
Archaeologists have been excavating Monte Verde on and off for almost 50 years, . One of the most prominent is at Vanderbilt University in Nashville, Tennessee. He and his colleagues have excavated two relatively close sites, simply dubbed Monte Verde I and Monte Verde II.
Monte Verde I is tricky. It contains burned areas and numerous putative stone artefacts – although some may simply be natural stones, albeit unusual ones. Early studies radiocarbon dating the charcoal placed the site as , which has never been widely accepted. In a 2015 study, Dillehay’s team dated Monte Verde I to . However, because the human traces are so sparse, the older end of that range is disputed, and Dillehay himself doesn’t put too much store by it.
Stronger evidence comes from Monte Verde II. Here, the team found , as well as what seem to be the foundations for a structure, perhaps a tent. Directly above the layers containing these materials was a layer of peat, which Dillehay’s team dated to 14,500 years ago. This implies that Monte Verde II is at least that old. In 1997, a team of archaeologists visited the site and . Subsequent evidence has supported the dating: for instance, in 2008, Dillehay’s team identified at Monte Verde II, which they directly dated to 14,220 to 13,980 years ago.
Today, Dillehay says, the evidence for the age of Monte Verde consists of “more than 1000 radiocarbon and luminescence dates and intact chrono-stratigraphy, as well as diagnostic stone tools dated in other sites”.
These finds at Monte Verde II effectively detonated our main ideas around the peopling of the Americas. For much of the 20th century, most archaeologists believed that the first Americans were peopled dubbed the Clovis, after a site in New Mexico. Clovis peoples made distinctive pointed stone tools. The oldest Clovis sites are about 13,000 years old.
So strong was the consensus around the Clovis First model that any pre-Clovis site came under immense scrutiny. Sites like Cooper’s Ferry, Buttermilk creek and Paisley caves in North America have been endlessly picked over. Monte Verde was the first site to survive this process and become established.
In March this year, another team of archaeologists tried to tear the whole edifice down.
Younger than that
first learned about Monte Verde in 1994, when he was an undergraduate at the University of Wisconsin. Dillehay came as a guest speaker to talk about the site. “I was absolutely blown away,” says Surovell. “It really inspired my career.”
Surovell is now an archaeologist at the University of Wyoming. Increasingly sceptical about Monte Verde, Surovell and his colleagues visited the area in 2022 and 2023. .
His team didn’t excavate at Monte Verde I or II, but along the banks of Chinchihuapi creek. Based on the layers of sediments they found, they reconstructed a history of the area.
About 20,000 years ago, they say, when Earth’s climate was deep in a glacial period, the region was the outwash from a glacier extending down from the Andes: a plain with braided streams and lots of sand and gravel. Later, as the climate warmed, a forest moved in, transitioned into a wetland, and was then buried – forming a black peat. Then, around 11,000 years ago, a volcano called Michinmahuida erupted and blanketed the area in a layer of ash, called the Lepué Tephra. Afterwards, Chinchihuapi creek cut down through all these layers, forming an exposed surface where people lived.
This means that Monte Verde II must be younger than the Lepué Tephra ash layer, Surovell’s team argues. Based on dating of sands and gravels at their excavation sites, they place it between 8200 and 4200 years ago.
To say this has caused a row would be an understatement. The Science paper now has seven “eLetters” attached to it, . On 19 August, Dillehay and his colleagues published in the journal PaleoAmerica, rebutting Surovell’s team’s arguments.
A central problem with all this is that Surovell’s team excavated near Monte Verde but not actually at it. Or, as Dillehay puts it: “They did not excavate at the site, never saw the stratigraphy and examined only surface landscape from 50 to 4000 meters away in distance.” Because this is a flood plain, where rivers shift over time and sediments can be mixed, extrapolating from one place to another is tricky.
For instance, Surovell’s team identified a layer of peat, which they say corresponds to the peat overlaying the Monte Verde II occupational layer. Dillehay’s team says it doesn’t.
Likewise, one of the key planks of evidence supporting Monte Verde’s age is the large quantity of wood at the site, which has been dated. “There’s a lot of wood in there that dates to the ice age, but that wood is derived from… older deposits,” argues Surovell. “It was eroded from these older deposits to wash into the stream onto these younger surfaces.” However, Dillehay argues that the wood shows no sign of having been redeposited – for example, there is no telltale damage from being bashed around in flood water.
Furthermore, there is no sign of the crucial Lepué Tephra ash layer at Monte Verde II, either above or below the layer with the artefacts. Dillehay argues that, therefore, it can’t tell us anything about the age of the site.
And so the argument goes on, for thousands of words and many more lines of reasoning. I have tried to pull out the main points, but I can’t overemphasise how much of a rabbit hole this is. Every detail of Dillehay’s and Surovell’s excavations is being picked over.
When a scientific claim becomes disputed, resolving who is correct can become extremely challenging, because of the “experimenter’s regress”. If we don’t know the true answer to some question, then it is difficult to judge whether we have performed an experiment correctly. If you get a surprising result, maybe you have found something new, or maybe you screwed up the experiment.
So, if an experiment contradicts your favoured theory about the world, you can simply argue that the experiment was flawed, or that the people who ran it are incompetent. The trouble is that they can say the same thing about your experiment. Hence the experimenter’s regress: a seemingly endless cycle of claim and counterclaim, with each side arguing that the other is stuffing up their research in crucial ways.
I’m not in a position to break the cycle here and call the correct answer. For one thing, I don’t feel confident judging whether the peat layer at Monte Verde II and the peat layer Surovell’s team found are, or aren’t, the same thing.
Pre-Clovis peoples?
Can we instead answer the question with independent lines of evidence? As I mentioned, there are now a lot of pre-Clovis sites in the Americas, and more turn up fairly regularly. Some of the most dramatic recent discoveries have been at White Sands National Park in New Mexico, where footprints and drag marks have been found that seem to be about . Meanwhile, genetic studies of Indigenous Americans and their Asian relatives seem to indicate people moving into the Americas around 15,000 years ago. One interpretation is that there were some early wanderers who didn’t survive, followed by at least one major migration.
This would seem to imply that people were in the Americas before the Clovis era, regardless of the truth about Monte Verde.
Surovell, for his part, argues that “the evidence for pre-Clovis in North and South America is not very good anywhere” and that “every other one of these sites has been questioned, and every other one of these sites is still in play”. He contends that “there are a heck of a lot of people in my field who you don’t hear from very much in the press”, who think the pre-Clovis sites are too poor in quality to be trusted. “I predict that you’re going to very much see archaeologists increasingly migrating back towards the Clovis First position.”
Meanwhile, Dillehay remains confident. “We just finished having an independent group of geologists and archaeologists at the site… who saw the stratigraphy, confirmed our work and pointed out the major errors of Surovell et al,” he says. “They will be publishing the results soon.”
I don’t know which of these predictions will prove more prescient, but I will say that I thought this question had largely been settled, and I am interested to see if people like Surovell succeed in reopening it.
