Analysis: A new study says settlers arrived in the Americas 130,000 years ago. Should we believe it?

Twenty-four years ago, construction workers building a new highway near San Diego stumbled upon a skeleton that may rewrite the entire history of the Americas.

Researchers found signs of human manipulation on the 130,000-year-old remains of a mastodon — an ancient and extinct relative of the elephant — at what’s now called the Cerutti Mastodon site, they said in a study published Wednesday in Nature. Here’s the rub. Almost all previous evidence points to humans arriving in the Americas approximately 20,000 years ago. This discovery could change that.

A view of two mastodon femur balls, one faced up and once faced down. Neural spine of a vertebra exposed (lower right) and a broken rib (lower left). Photo by San Diego Natural History Museum

Needless to say, this report has sparked controversy, like “paleontologists-all-over-America-pulling-out-their-hair” controversy. Here’s what you need to know.

What they found:

• Starting in the winter of 1992, Richard A. Cerutti and other paleontologists from the San Diego Natural History Museum began excavating the Cerutti Mastodon site.
• The team discovered bones from a young adult male mastodon — tusks, molars, vertebrae, ribs, paw bones and more than 300 fragments — centered around a large cobble stone. The researchers also found wear-and-tear patterns on other stones that suggest they were used as hammers In the last five years, researchers used uranium dating to determine the bones were 130,000 years old. They couldn’t use traditional carbon dating because the mastodon’s collagen had eroded.
• “It makes ours the oldest archaeological site in the Americas — older by a factor of 10,” San Diego Natural History Museum paleontologist and study coauthor Thomas Deméré at a press briefing Tuesday. “Currently the oldest widely accepted date of human presence in the new world is 14,000 to 15,000 years ago.”

Why you should believe this finding:

• Spiral-fracture patterns on the mastodon bones suggest they were broken soon after the mastodon died
• Only long bones like femurs showed fractures, whereas more fragile bones like the ribs were intact. If more recent, wholesale disturbances — like cars or large construction machinery trundling over the buried archaeological site — had broken the bones, then the ribs would likely have fractures, too.
• Study co-author Steven Holen of the Center for American Paleolithic Research in Hot Springs, South Dakota said there was also no evidence of other natural processes, like:
  • Geologic disruption: Surrounding sediments were relatively light, so wouldn’t have caused bone breakage. Also the sediments exhibited “low-energy deposition,” meaning water hadn’t tossed around the bones and led to these breaks.
  • Animals trampling on the bone: Trampling tends to produce different breaks, and past studies suggest trampling doesn’t normally occur near elephant death sites
  • Carnivore chewing: Carnivores gnaw on the ends of bones, while these mastodon bones were broken in the middle.)
• The mastodon bone fractures mirror those seen when elephant bones are shattered with large hammers, rock hammers and rock anvils, as in previous archaeological finds in Africa and recreation experiments conducted by the team. People in Africa have been breaking up elephant limb bones with this pattern for 1.5 million years, Holden said.
• “What’s truly remarkable about this site is you can identify a particular hammer that was smacked on a particular anvil,” said University of Wollongong archaeologist Richard Fullagar, a coauthor on the study who specializes in stone artifacts. “The fragments of those hammers and anvils can then be refitted to the stones.”

A boulder discovered at the Cerutti Mastodon site thought to have been used by early humans as a hammerstone. Photo by Tom Deméré, San Diego Natural History Museum

Why you should be skeptical:

• Genetic analysis of human remains, collected outside the current study, have long suggested that Native American populations are linked to early humans who crossed the Bering land bridge from Siberia and settled in the Americas about 15,000 to 20,000 years ago.
• No human remains were found at the Cerutti Mastodon site. That isn’t too surprising, given human remains in extremely old geologic deposits are rare. Researchers, for instance, have only found two examples of human remains for the Clovis culture, which existed about 13,000 years ago in the Americas.
• Due to warmer temperatures and sea level rise, the Bering land bridge should have been underwater 130,000 year ago. So these humans either crossed earlier, or made some portion of the journey by boat. Elsewhere in the world during this time period, early humans had popped up on the islands of Crete and Sulawesi. So, the use of watercrafts isn’t beyond the realm possibility. Also, neanderthals lived in
• John McNabb, a Palaeolithic archaeologist at the University of Southampton, UK, told Nature News that it’s curious the site “yielded no other traces of human presence,” such as those related to animal butchery.

If the study holds up, what happened to these “Cerutti” Americans?

• It’s entirely possible that these early Americans became extinct, Holen said. Present-day Amazonian Native Americans also carry a set of genetic markers that are unlike those found in Central and Northern populations. These markers hail from Asian islanders, suggesting there were two founding populations for the Americas, but it’s unclear when the second group arrived.
• This latest Cerutti Mastodon site is hardly the first to try rewrite early American history, wrote Hebrew University of Jerusalem archaeologist Erella Hovers, who penned an op-ed also published Wednesday by Nature:

The best-known and controversial archaeological claims for early human entry into the Americas are from the Calico Hills in California (originally thought to be 80,000–50,000 years old or even older), Pedra Furada in Brazil (40,000−20,000 years old) and Old Crow in the Yukon Territory of Canada.

However, the interpretations of site context, the nature of the stone items, and the human ‘signature’ on fossil faunas offered in support of these claims have been criticized.

In these cases, the findings could be explained as the outcome of geological or biological processes that superficially mimic human-made items, or the associations of the dated sediments with the artefacts are questionable.

***Time will tell whether this evidence will bring a paradigm change in our understanding of processes of hominin dispersal and colonization throughout the world (including in what now seems to be a not-so-new New World).