Discovery is further proof that Indigenous people have been in the Americas longer than archaeologists once thought.
Buried deep beneath a layer of volcanic ash, archaeologists excavating Rimrock Draw Rockshelter in Oregon 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.
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.
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.