It's not clear what species of hominid they belonged to. Bogdan Sonjachnyj/Shutterstock

Each and every scientific discovery sends a small ripple through academia – it changes what we know about the world around us in a fundamental but usually quite subtle way. A breathtaking new study in Nature, however, is more of a tidal wave, a revolution in the way we understand the story of humanity.

The general consensus has been that humans arrived in North America no later than 24,000 years ago, at the earliest. A startling archaeological discovery of ancient human activity in California, however, has possibly moved this date back to 131,000 years, and in the process has potentially rewritten the history books.

“Extraordinary claims require extraordinary evidence,” co-author Richard Fullagar, Honorary Principal Fellow at the University of Wollongong, told IFLScience on a conference call. “The dates are truly remarkable, but it’s hard to argue with the clear evidence we see. It’s incontrovertible.”

A deeply-buried site in coastal San Diego County contained the remains of a mastodon, an extinct creature distally related to elephants, including several tusks with curious indentations on them. On closer inspection, these marks appeared to perfectly match up with various hammerstones, anvils, and tools found nearby.

No actual human remains were found, which means that this study is likely to generate some criticism from other archaeologists. Nevertheless, these tools resembled those being used by humans and their ancestors all over the planet, before and since. Using a series of experiments that recreated the hammering and cutting activity the tools were presumably used for on the mastodon remains, the team perfectly recreated the indentations.

A mastodon skull. Brooke Crigger/Shutterstock

“What’s truly remarkable here is that you can match the hammers to the anvils to the stones – it really does demonstrate human interference,” Fullagar noted.

State-of-the-art uranium dating techniques revealed without question that these tusks were 131,000 years old, as were the marks on them. No known carnivore or geological process could have made such precise scratches on them, and the site itself had remained undisturbed by erosional processes since it appeared.

Ruling everything else out, and approaching their assessment of the find as carefully and as conservatively as possible, the team concluded that this was an archaeological site.

The First Americans. Nature Video via YouTube

A mastodon was killed and some of its remains were moved here, where ancient humans or human ancestors began carving up the tusks for use as tools, ornaments or to extract the bone marrow for food – an ancient human activity that dates back at least 1.5 million years to African settlements.

The date completely tears up everything we knew about human migration across the world.

“I expect there will be some extraordinary claims about how they got there,” co-author Steven Holen, Co-Director of the Center for American Paleolithic Research, added. “We expect criticism, and we are ready for it. I was skeptical when I first looked at it myself, but it’s definitely an archaeological site.

Some of the possible migration routes. Note, starting points do not necessarily indicate speciation points. Chris Jones/IFLScience