These are the oldest stone tools ever found in the United States

Stone tools unearthed from a rock shelter in Southern Oregon were last used more than 18,000 years ago, radiocarbon dating suggests. That makes the site one of the oldest-known human living spaces in the Americas. But the people who lived in Oregon more than 18,000 years ago almost certainly weren’t the first to call the continent home.

A home where the buffalo roam

Buried deep beneath a layer of volcanic ash, archaeologists excavating Rimrock Draw Rockshelter found two stone scraping tools, which ancient knappers had skillfully shaped from pieces of orange agate. A residue of dried bison blood still clung to the edges of one scraper, a remnant of the last bit of work some ancient person had done with the tool before discarding it. The layer of volcanic ash above the tools had blasted out of Mount St. Helens, a few hundred kilometers north of the rock shelter, 15,000 years ago, long after the fine agate scrapers, and the people who made and used them, had been forgotten.

But how long?

In a layer of dirt below the volcanic ash but above the stone tools, archaeologists found broken teeth from now-extinct relatives of modern camels and bison. Radiocarbon dating on a piece of bison tooth enamel (first in 2012, and confirmed recently by more testing) suggests the teeth belonged to animals that lived about 18,250 years ago. And because those teeth were buried in a layer of dirt above the stone tools, they must have ended up in Rimrock Draw sometime after the tools. That makes the agate scraper, complete with bloody evidence of its use, more than 18,000 years old—and one of the oldest traces of human presence in North America.

New ideas about old events

“The identification of 15,000-year-old volcanic ash was a shock,” said University of Oregon archaeologist Patrick O’Grady, who runs an archaeological field school at the site. “Then [data from Tom Stafford of Stafford Research] 18,000-year-old dates on the enamel, with stone tools and flakes below, were even more startling.”

A decade ago, archaeologists would have been completely flabbergasted to find evidence that people were living in North America 18,000 years ago. At that point, the oldest evidence of people anywhere on the continent dated to around 13,000 years ago, in the form of long projectile points with flutes: narrow notches at their bases, creating a shallow groove to fit a wooden shaft for hafting.

These points belonged to people we now call the Clovis Culture. And for most of the 20th century, it looked like the Clovis people were the first ones to arrive in North America, probably following a huge gap in the middle of the kilometers-thick ice sheet that covered most of what’s now Canada and the northern US.

But today, the “Clovis First” theory is now just part of the history of science. The stone tools at Rimrock Draw are just the latest in a growing pile of evidence that people arrived in North America thousands of years before the ice sheets opened enough to create an ice-free corridor down the middle of the continent. Most archaeologists who study how people first reached the Americas now agree that they probably followed the edge of the ice sheet along the western coast of Canada sometime between 20,000 and 16,000 years ago.

Following the edge of the ice

In Idaho, the Nimiipuu (Nez Perce) know the Cooper’s Ferry archaeological site as the ancient location of a village they call Nipehe. The oldest artifacts unearthed at the site date to at least 16,000 years ago, and it looks like people lived there, at least off and on, for several thousand years after those first arrivals. To have reached Cooper’s Ferry 16,000 years ago, the ancient inhabitants of Nipehe would have had to cross Beringia, a land mass that connected what’s now Russia with what’s now Canada during the last Ice Age, when sea levels were lower. They then had to move south along the Pacific Coast of North America, skirting along the western edge of the great ice sheet, until they reached the southern edge of the ice.

The ice-free corridor wouldn’t open until about 15,000 to 14,000 years ago. By then, people were already living far, far south of the ice: Archaeologists found stone tools and butchered mastodon bones submerged in a Florida sinkhole that dated back to 14,500 years ago. And in Chile, someone left behind a single footprint 14,600 years ago.

Thanks to footprints on an island off the coast of what’s now British Columbia, we know that at least some people did make their way along the coasts about 13,000 years ago. But some archaeologists, like Bournemouth University’s Matthew Bennett and his colleagues, say that those coastal migrants may have found their way into a continent already home to people who arrived at least 26,000 years ago—long before the ice sheets blocked the way into North America from Asia.

In the mountains of north-central Mexico, archaeologists unearthed stone tools from Chiquihuite Cave, which dated back to around 30,000 years ago. And at White Sands National Monument in New Mexico, it appears that someone walked along the ancient shoreline of Lake Otero (now long since dry) between 23,000 and 21,000 years ago, leaving behind a trail of 61 footprints. Archaeologists dated the White Sands footprints thanks to grass seeds trapped in the layers of clay and silt above and below the tracks, which helped bracket their possible age.

Some archaeologists are still skeptical, partly because there are so few sites this old south of the ice sheets. But there’s enough evidence to take the claims seriously.

Peopling a continent is complicated

The only way to really pin down when, where, and how the first people set foot in the Americas is to gather more evidence. Many of the oldest archaeological sites in the Americas are probably underwater now, submerged by rising seas at the end of the last Ice Age. But evidence from sites farther inland could still shed enough light on the subject to tell us whether—to give just one example—people arrived in waves before, during, and after the Last Glacial Maximum or if everyone arrived at more or less the same time.

Over the next few years, new discoveries and new research at sites like Cooper’s Ferry and Rimrock Draw might also help archaeologists piece together where these first Americans hailed from and how they lived. At Cooper’s Ferry, for example, people were using stone tools that look strikingly similar to the ones people were using at around the same time on the Japanese island of Hokkaido. They even appear to have used the same knapping techniques to make the tools. It’s possible that the people who dug hearth pits in Idaho 16,000 years ago may have been related—albeit maybe several generations removed—to people living very similar lives in Hokkaido.

Meanwhile, the stone tools from Chiquihuite Cave look nothing like any other stone tool culture anywhere in North America, which means the people who made the tools 30,000 years ago may have traced their cultural roots to a completely different group of people than those who settled at Cooper’s Ferry, Clovis, or Rimrock Draw. The more we learn about the early past of the Americas, the more complicated and dynamic the picture gets.

Archaeologists at Rimrock Draw will spend the rest of this summer excavating other parts of the site, where a University of Oregon press release claims “more Ice Age animal remains and artifacts are providing supporting evidence for the [stone tool] discoveries.” Meanwhile, other archaeologists are radiocarbon dating more of the camel and bison teeth and studying plant remains unearthed from ancient cooking fires.