Archaeologists have uncovered almost two hundred stone artifacts, including projectile points and flake tools, and bone fragments from large mammals at the Cooper’s Ferry site in western Idaho, the United States. The discovery suggests that humans lived in the area 16,000 years ago, more than a thousand years earlier than scientists previously thought. They therefore arrived in the Americas before an inland ice-free corridor had opened. The projectile points from the site closely resemble those found in Japan, supporting the hypothesis of a Pacific coastal route.

The Cooper’s Ferry site is located within a terrace at the confluence of Rock Creek and the lower Salmon River of western Idaho. The Nez Perce Tribe refers to this place as an ancient village site named Nipéhe.

“This site is located along the Salmon River, which is a tributary of the larger Columbia River basin,” said Oregon State University’s Professor Loren Davis.

“Early peoples moving south along the Pacific coast would have encountered the Columbia River as the first place below the glaciers where they could easily walk and paddle in to North America.”

“Essentially, the Columbia River corridor was the first off-ramp of a Pacific coast migration route.”

“The timing and position of the Cooper’s Ferry site is consistent with and most easily explained as the result of an early Pacific coastal migration.”

The team unearthed 189 stone artifacts, including 27 stone tools (projectile points, biface fragments, blades, and flake tools).

They found charcoal, a fire-cracked rock, and 86 bone fragments likely from medium- to large-bodied animals.

They also found evidence of a fire hearth, a food processing station and other pits created as part of domestic activities at the site.

Many artifacts from the Cooper’s Ferry site 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,” Professor 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,” Professor Davis said.

“Now we have good evidence that people were in Idaho before that corridor opened. This evidence leads us to conclude that early peoples moved south of continental ice sheets along the Pacific coast.”

The researchers 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,” Professor 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,” he added.

The findings appear online this week in the journal Science.

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Loren G. Davis et al. 2019. Late Upper Paleolithic occupation at Cooper’s Ferry, Idaho, USA, ~16,000 years ago. Science 365 (6456): 891-897; doi: 10.1126/science.aax9830