Humans may have arrived in North America 115,000 years earlier than researchers thought

Researchers may have been off by nearly 115,000 years when they estimated that humans arrived in North America about 15,000 years ago. The potential miscalculation was uncovered by a collection of mastodon bones, which were discovered during construction work on a California freeway in 1992. After toiling for years to date the bones, researchers announced this week in a paper published in the scientific journal Nature that they'd determined the remains of the adult male mastodon to be about 130,000 years old — and to contain signs of human activity.

The finding is likely to be controversial. Already, Smithsonian Magazine noted, the question of when humans arrived in North America is "a flashpoint among archaeologists." There is no other evidence to indicate humans arrived tens of thousands of years earlier than has been suggested, but paleontologist Thomas Deméré, one of the study's authors, said they have the evidence to back up the claim. "I realize that 130,000 years is a really old date," Deméré said. "Of course, extraordinary claims like this require extraordinary evidence."

The mastodon bones that were uncovered bear "impact marks suggesting that they had been smacked with a hard object," Smithsonian Magazine reported. Researchers also discovered five massive stones at the site, which they believe humans may have used as hammers or anvils. The stones "showed signs of impact," Smithsonian Magazine said, and the bones were found piled up right around these stones.

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"[W]e can eliminate all of the natural processes that break bones like this," said Steven Holen, another study co-author. "These bones were not broken by carnivore-chewing, they were not broken by other animals trampling on the bone."