The remains of a mastodon found in California have revealed that humans may have been in North America earlier than previously thought.
Researchers with the San Diego Natural History Museum said in a newly released paper that the remains of a mastodon that were found in 1992 during a freeway excavation in San Diego show signs of human activity in North America 120,000 to 140,000 years ago, according to National Geographic.
"I realize that 130,000 years is a really old date and makes our site the oldest archaeological site in the Americas," said paleontologist Tom Demere of the team that analyzed the remains. "Of course, extraordinary claims like this require extraordinary evidence, and we feel like the Cerutti mastodon site presents this evidence."
While the team did not find human remains at the site, they did find several large stones alongside the mastodon skeleton, and flakes of bone. The team has put forward that the site was once a "bone quarry," where early humans mined mastodon bones for materials with stone hammers.
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"This is a whole new ball game," said Steve Holen, the paper's lead author who co-directs the Center for American Paleolithic Research.
"The bones and several teeth show clear signs of having been deliberately broken by humans with manual dexterity and experiential knowledge," he told CNN.
While most experts had previously placed the first human activity in North America at around 15,000 years ago, the new findings from the Cerutti mastodon "shows that human ancestors were in the New World 10 times that length of time," paleontologist Lawrence Viscera said.
"This site really nails it because the evidence is really clear," Viscera added.
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Other experts have said that they are skeptical about the paper's claims.
"The earliest occupation of the Americas is a highly contentious subject," said archaeologist John McNabb. "The date of the find at 130,000 years ago is a really big ask for archaeologists who are used to talking about 12, 13, 14,000 years ago. It's a big, big time difference."
According to archaeologist Tom Dillehay, it's possible that natural processes carried the stones to the site -- and, he added, the paper does not fully rule out the possibility of nature wearing down the stones.
"When you put the total package together, there’s certainly more evidence to reject [the study] than accept it," said Dillehay.
Holen says the team has "made a very good case that this is an archaeological site," and is "quite prepared for the firestorm that's coming."