An ancient stone tool, carved from a piece of agate, was recently uncovered in the high desert of Oregon. Most significantly, the tool was unearthed from beneath an undisturbed layer of ash linked to a Mount St. Helens eruption 15,800 years ago.

"When we had the volcanic ash identified, we were stunned because that would make this stone tool one of the oldest artifacts in North America," excavation leader Dr. Patrick O'Grady, an archaeologist at the University of Oregon, said in a press release. "Given those circumstances and the laws of stratigraphy, this object should be older than the ash."

The tool was recovered from a deposit known as Rimrock Draw Rockshelter, located in southeastern Oregon.

If confirmed, the finding would make the tool the oldest human-related artifact in North America. It would also change archaeologists' understanding of the settlement of the continent. It's been previously suggested that North America's first humans arrived around 13,500 years ago -- a civilization known as the Clovis people, linked by a style of tools found in the Southwest near Clovis, N.M.

Last week, scientists were able to analyze the tool for blood residue. Test results revealed the remains of an extinct species of bison (Bison antiquus), a relative of the modern buffalo. It's likely the tool was used for scraping animal hides

"The discovery of this tool below a layer of undisturbed ash that dates to 15,800 years old means that

this tool is likely more than 15,800 years old, which would suggest the oldest human occupation west of the Rockies," explained Scott Thomas, an archaeologist with the Bureau of Land Management.

Of course, until the scientific paper detailing the tool and its discovery is peer reviewed, there will be doubts about the date. Additional digs may help to quiet critics who suggest a break in the ash layer may have allowed younger artifacts to slip below it.

"We'll be working to find more of that ash layer -- and investigating what's beneath it -- in additional portions of the site," O'Grady added.

Excavations will continue at Rimrock through the summer.