Artifacts from the Cooper’s Ferry site poke more holes in the traditional theory of when people arrived in the Americas
Until a couple decades ago, Clovis stone tools, which are generally about 13,000 years old, were considered to be the first human technology in the Americas.
As part of the “Clovis-first” hypothesis, most researchers believed that the people who made these tools first entered North America on foot from Asia by crossing Beringia, the stretch of land that once connected Siberia and Alaska, and traveling down an ice-free corridor that opened up when massive ice sheets that once covered the interior of North America began to retreat roughly 14,000 years ago.
However, a small but growing body of research has suggested people were present in the Americas centuries before this ice-free corridor existed, with some radiocarbon dates hinting at sites up to nearly 15,000 years old and other less reliably dated sites going back 16,000 years, said study lead author Loren Davis, an archaeologist at Oregon State University in Corvallis.
This has led some researchers to suggest the earliest migrants came in boats along the Pacific coast, living off fish, kelp and other marine resources.
In the new study, Davis and his colleagues investigated Cooper’s Ferry, an archaeological site located in the lower Salmon River canyon in western Idaho. Excavations can prove challenging — “summer temperatures are hot, up to 120 degrees Fahrenheit, and we have to bring water from afar to our camp each week,” Davis said. Moreover, “we are always on the lookout for rattlesnakes and black widow spiders.”
Over the past two summers, the scientists reached the site’s bottom layers, which they expected to contain its earliest artifacts. They radiocarbon dated animal bone fragments from this layer and found that humans may have occupied the site as early as roughly 16,560 years ago.
“This may be among the earliest evidence of occupation of the Americas yet,” Davis said. “If one had to explain why there were people in Idaho before continental ice sheets had a breach in them through which one could walk north to south, the most parsimonious explanation might be they came down the coast.
It may be no coincidence that if one moved down along the Pacific Coast and then went down the Columbia River into the interior of North America, after a while, if they made a lefthand turn, it would not take too long to get to the Cooper’s Ferry site.”
Cooper’s Ferry, located at the confluence of Rock Creek and the lower Salmon River, is known by the Nez Perce Tribe as an ancient village site named Nipéhe. Today the site is managed by the U.S. Bureau of Land Management.
Davis first began studying Cooper’s Ferry as an archaeologist for the BLM in the 1990s. After joining the Oregon State faculty, he partnered with the BLM to establish a summer archaeological field school there, bringing undergraduate and graduate students from Oregon State and elsewhere for eight weeks each summer from 2009 to 2018 to help with the research.
The site includes two dig areas; the published findings are about artifacts found in area A. In the lower part of that area, researchers uncovered several hundred artifacts, including stone tools; charcoal; fire-cracked rock; and bone fragments likely from medium- to large-bodied animals, Davis said. They also found evidence of a fire hearth, a food processing station and other pits created as part of domestic activities at the site.
Over the last two summers, the team of students and researchers reached the lower layers of the site, which, as expected, contained some of the oldest artifacts uncovered, Davis said. He worked with a team of researchers at Oxford University, who were able to successfully radiocarbon date a number of the animal bone fragments.
The results showed many artifacts from the lowest layers are associated with dates in the range of 15,000 to 16,000 years old.
“Prior to getting these radiocarbon ages, the oldest things we’d found dated mostly in the 13,000-year range, and the earliest evidence of people in the Americas had been dated to just before 14,000 years old in a handful of other sites,” Davis said.
“When I first saw that the lower archaeological layer contained radiocarbon ages older than 14,000 years, I was stunned but skeptical and needed to see those numbers repeated over and over just to be sure they’re right. So we ran more radiocarbon dates, and the lower layer consistently dated between 14,000-16,000 years old.”
The dates from the oldest artifacts challenge the long-held “Clovis First” theory of early migration to the Americas, which suggested that people crossed from Siberia into North America and traveled down through an opening in the ice sheet near the present-day Dakotas. The ice-free corridor is hypothesized to have opened as early as 14,800 years ago, well after the date of the oldest artifacts found at Cooper’s Ferry, Davis said.
“Now we have good evidence that people were in Idaho before that corridor opened,” he said. “This evidence leads us to conclude that early peoples moved south of continental ice sheets along the Pacific coast.”
Davis’s team also found tooth fragments from an extinct form of horse known to have lived in North America at the end of the last glacial period. These tooth fragments, along with the radiocarbon dating, show that Cooper’s Ferry is the oldest radiocarbon-dated site in North America that includes artifacts associated with the bones of extinct animals, Davis said.
The oldest artifacts uncovered at Cooper’s Ferry also are very similar in form to older artifacts found in northeastern Asia, and particularly, Japan, Davis said.
He is now collaborating with Japanese researchers to do further comparisons of artifacts from Japan, Russia and Cooper’s Ferry. He is also awaiting carbon-dating information from artifacts from a second dig location at the Cooper’s Ferry site.
“We have 10 years’ worth of excavated artifacts and samples to analyze,” Davis said. “We anticipate we’ll make other exciting discoveries as we continue to study the artifacts and samples from our excavations.”
Co-authors of the paper include David Sisson, an archaeologist with the BLM; David Madsen of the University of Texas at Austin; Lorena Becerra Valdivia and Thomas Higham of the Oxford University radiocarbon accelerator unit; and other researchers in the U.S., Japan and Canada. The research was funded in part by the Keystone Archaeological Research Fund and the Bernice Peltier Huber Charitable Trust.