Mastodon tenderizers shift human history in North America wayyy back… again.

Science News reports on a twisty debate on human origins in North America, with a new analysis of stones embedded with microscopic bits of mastodon, apparently used by prehistoric chefs 130,000 years ago:

In 2017, scientists reported that around 130,000 years ago, an unidentified Homo species used stone tools to break apart a mastodon’s bones near what is now San Diego. If true, that would mean that humans or one of our close evolutionary relatives reached the Americas at least 100,000 years earlier than previously thought, dramatically reshaping scientists’ understanding of when the region was settled.

Chemical residue of bones appears on two stones previously found among mastodon remains at the Cerutti Mastodon site, the scientists report in the December Journal of Archaeological Science: Reports. The two Cerutti rocks also show signs of having delivered or received hard blows where bone residue accumulated, the team says. The larger stone may have served as a platform on which the bones were smashed open with the smaller stone, possibly to remove marrow for eating or to obtain bone chunks suitable for shaping into tools.

In the new study, [University of Wollongong geoarchaeologist Richard] Fullagar, Wollongong geoarchaeologist Luc Bordes and colleagues used microscopes to determine that the chemical and molecular structure of residue on the two stones matched that of bones in general. That residue must have been acquired by pounding apart mammoth bones that were found scattered around the stones, the team argues. Since microscopic remnants of bone appeared only where stones showed signs of wear and hard impacts, it’s unlikely that the stones accumulated the residue by accidentally coming in contact with mastodon bones after being covered by sediment, the scientists say.