When did humans arrive in the Americas? A new study reignites the debate

On the banks of a creek flowing through temperate rainforest in southern Chile, a small group of hunter-gatherers camped briefly, maybe for a few months. When they departed, they left behind several clues into their daily lives, including chipped stone spearpoints, butchered mastodon ribs, and at least one human footprint in hardened clay.

The discovery of the ancient campsite, called Monte Verde, shook the archaeological world in the 1970s as it overturned long-held assumptions about when and where the first humans arrived in the Americas. The initial radiocarbon dates from the site suggested its artifacts may be the earliest evidence of humans in the Americas uncovered at that point. It also forced archaeologists to rethink how humans came to the Americas—including the possibility that some may have arrived by boat instead of by land. 

New research published Thursday in the journal Science challenges the prevailing theory of Monte Verde’s antiquity and reignites discussions about the timing of the first Americans.

It’s the last, major mysterious migration chapter in our human origins story. Scientists know that Homo sapiens arose in Africa around 300,000 years ago, then moved into Europe and Asia starting around 100,000 years ago, and only much later arrived in the New World.

“Suddenly, the iconic site that transformed our thinking about when and how the first people came to the Americas is being disputed with what seems like very convincing evidence,” says Ted Goebel, an archaeologist at the University of Kansas who was not involved in the new research. “It’s going to be a really interesting debate over the next few months and years,” Goebel adds. “It’ll be a firestorm.”

Revisiting an iconic discovery

The land near Monte Verde is rolling green countryside with no visible evidence of ancient encampments. But when the original researchers heard that locals had stumbled across an exposed mastodon tooth, they knew to start digging.

Monte Verde’s discovery was a scientific sensation because radiocarbon dates of wood fragments and other organic materials found near the stone tools suggested the site was around 14,500 years old. That hinted it could be 1,500 years older than North America’s Clovis culture, which had been the long-standing benchmark for the earliest human presence in the Americas, distinguished by fluted spearpoints first found in New Mexico.

(Tracking the First Americans)

“Monte Verde totally changed the discussion,” says Mírian Liza Alves Forancelli Pacheco, an archaeologist at Brazil’s Federal University of São Carlos who was not involved in the new study. “It made people think again and ask new questions about other archaeological sites, including in South America,” she says.

In the new Science study, the first independent team of researchers to assess Monte Verde in 50 years suggests the site may be much younger than previously thought, perhaps less than 8,000 years old.

When study co-authors Todd Surovell and Claudio Latorre Hidalgo first visited Monte Verde in early 2022, they noticed it was situated on the floodplain of a meandering prehistoric stream, now called Chinchihuapi Creek.

Their analysis of the geology suggests that the stream changed course during a hot and dry climatic phase, around 10,000 years ago, says co-author Latorre, a paleoecologist at the Pontifical Catholic University of Chile. When sea level dropped, the stream cut a deeper course through the hillside, picking up well-preserved fragments of Ice Age wood and other organic materials, exposed by glacial retreat, and redepositing them near the archaeological site. This, they argue, may have contaminated earlier efforts to date the site.

“When we’re dating wood, we’re dating when that wood formed. That’s not the same thing as dating when people lived there,” says co-author Surovell, an archaeologist at the University of Wyoming. “This is an old wood problem.”

Several outside experts say the evidence looks compelling.

“The argument is very simple and convincing. They realized a typical erosion process that removed material from one place to another,” says Calogero Santoro, an archaeologist at the University of Tarapacá in Chile, who was not involved in the research.

(When, How Did the First Americans Arrive? It’s Complicated.)

“As far as I can see, the work is very well done. The analysis of the sedimentology and stratigraphy looks accurate,” says Thomas Stafford, a research geochemist and geochronologist at Stafford Research in New Mexico, who was not involved in the new paper. “It’s good that an entirely different group of people have come in and looked at this,” he adds.

The new researchers also looked at another line of evidence, identifying a layer of volcanic ash in outcroppings adjacent to the stream, where they believe the original stratigraphic sequence is preserved and not altered by streamflow. Based on the location of the ash, the Monte Verde artifacts must have been deposited more recently, they argue. Earlier research has identified the volcanic ash, which has a unique chemical signature and is known regionally, as being 11,000 years old.

But Tom Dillehay, a Vanderbilt University archaeologist and one of the original researchers to excavate Monte Verde, disputes the new findings. “Do you really think that 50 years of research at a place by more than 80 specialists from many different disciplines from around the world made such as big mistake?” he writes in an email.

Co-author Surovell acknowledges there will always be room to doubt because no one can repeat the original team’s excavation in precisely the same place.

“Archaeological excavation is destructive,” he says. “Once I dig a portion of a site, someone can’t go back and dig exactly what I did.”

The legacy of Monte Verde

If Monte Verde’s age is disputed, its seminal role in history is not.

Since Monte Verde, archaeologists have looked for, and found, many other archaeological sites older than Clovis in both North and South America, says Stafford.

One of those sites in New Mexico’s White Sands National Park preserves fossil footprints of humans crossing the paths of extinct megafauna, including mammoths, ground sloths, and dire wolves. Research published earlier in Science suggests the footprints may be between 21,000 and 23,000 years old, based on multiple lines of evidence.

The difference between a site being 13,000, 14,500, or 21,000 years old is significant because it raises other questions about how early humans arrived.

(Stunning footprints push back human arrival in Americas by thousands of years)

Monte Verde prompted archaeologists to look for explanations as to how people could get to the Americas before the emergence of an ice-free corridor in Canada that only arose near the end of the last Ice Age, around 13,800 years ago. That spurred research into coastal archaeological sites and possible evidence that staggered groups of early humans also arrived by boat along the Pacific Coast—what’s now called the kelp highway.

Some of those sites will likely now draw further scrutiny to ensure they have been correctly dated and that existing theories still hold up. However, most archaeologists think it’s still likely that people lived in the Americas before Clovis culture and that they arrived in waves of migrations, both overland and by sea.

“Just because Monte Verde might be wrong, it doesn’t mean the other early sites can be easily dismissed,” says Rio de Janeiro State University paleontologist Thaís Pansani, who was not involved in the new study.

She welcomes the debate. “This is science, it’s about disagreements and new perspectives,” she says.