Stone artefacts unearthed in Idaho could have belonged to some of North America’s first residents.Credit: Loren Davis

Projectile points and other stone tools recovered near a riverbank in Idaho suggest that ancient humans reached the western United States more than 16,000 years ago.

The finds make the site, called Cooper’s Ferry, one of the oldest-known human settlements in North America, if not the oldest, says Loren Davis, an archaeologist at Oregon State University in Corvallis, who led the 10-year excavation that made the discoveries. His team’s results were published in Science on 29 August1.

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Cooper’s Ferry joins a growing list of archaeological sites in North and South America that are overturning dogma about how and when the Americas were first settled. Overwhelming evidence now suggests that the region’s first inhabitants travelled from Asia along the Pacific Coast more than 16,000 years ago — and not via inland routes several thousand years later, say Davis and others.

For decades, most archaeologists had contended that humans first settled the Americas through an ‘ice-free corridor’ in central Canada created by glacial melt 12,000–13,000 years ago. This tallied with the appearance of stone tools at sites across North America — including distinct fluted arrowheads attributed to the ‘Clovis culture’, whose people were once thought to be the Americas’ first settlers.

But the discovery of earlier, pre-Clovis sites — including a nearly 15,000-year-old settlement called Monte Verde in southern Chile and the 14,000-year-old Paisley Caves in Oregon — challenged the theory that Clovis people were the first to reach the Americas. A pair of 2016 studies analysed ancient plant and animal DNA and concluded that the ice-free corridor was not habitable until 12,600–13,000 years ago2,3 — too late to explain the pre-Clovis archaeological sites.

Radiocarbon revelation

Davis first worked at Cooper’s Ferry, which is located beside a tributary to the Columbia River, in the late 1990s as part of his PhD work. In a small-scale excavation, his team discovered stone points that are distinct from Clovis projectiles and other signs of human occupation; these were provisionally determined to be as old as 13,300 years. “In the ’90s this was extremely contentious,” says Davis, because it pointed to a stone-tool technology as old as — if not older than — Clovis tools.

Between 2009 and 2018, his team excavated a larger area of Cooper’s Ferry, unearthing more stone artefacts, as well as dozens of discarded fragments from the tool-making process. By studying more of the site and its underlying geology, he hoped to get a more reliable estimate of its age through advanced radiocarbon dating techniques.

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“I was hoping we could evaluate if the site was really 13,300 years old,” says Davis. However, dating of charcoal and animal bones found alongside the artefacts suggested that the oldest occupation of Cooper’s Ferry began between 16,500 and 15,300 years ago, and that humans continued to live there for thousands of years afterwards. “It just absolutely blew our minds how early this stuff was,” Davis adds.

The site’s age adds to existing evidence that the first humans to settle the Americas travelled along its Pacific Coast. “People are in Idaho way too early to come through an ice-free corridor,” says Davis. “They would have been able to exit this coastal route and go off the Columbia River. It’s the first off-ramp.”

But Ben Potter, an archaeologist at the University of Alaska Fairbanks, says it’s not yet clear whether humans reached Copper’s Ferry by way of the Pacific or via the ice-free corridor. He questions whether the very oldest radiocarbon dates from the site are actually linked to human occupation and says that more work needs to be done to determine when humans lived there. “Cooper’s Ferry is intriguing, but not paradigm-shifting.”

Many archaeologists presume that migrations into the Americas were led by humans living in the now-submerged region, known as Beringea, that bridged eastern Siberia and Alaska. But Davis wonders whether humans from north-eastern Asia led the way by travelling around the Pacific Rim. The projectile points from Cooper’s Ferry are similar to those made by ancient humans in Japan 13,000–16,000 years ago, he notes.

David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas, says the dating of Cooper’s Ferry is “rock solid”. He just isn’t ready to accept that its artefacts are relics of migrations from Asia. “It’s still an open question as to what the earliest pre-Clovis technology looked like,” he adds.