In an announcement sure to spark a firestorm of controversy, researchers say they’ve found signs of ancient humans in California between 120,000 and 140,000 years ago—more than a hundred thousand years before humans were thought to exist anywhere in the Americas.

If the researchers are right, the so-called Cerutti mastodon site could force a rewrite of the story of humankind.

“I realize that 130,000 years is a really old date and makes our site the oldest archaeological site in the Americas,” says study leader Tom Deméré, the paleontologist at the San Diego Natural History Museum, whose team describes their analysis today in Nature. “Of course, extraordinary claims like this require extraordinary evidence, and we feel like the Cerutti mastodon site presents this evidence.”

To be clear, the team has not found human bones at the site. But as Deméré and their colleagues tell it, their evidence—a mastodon skeleton, bone flakes, and several large stones—shows that the area was a “bone quarry,” where an unknown hominin allegedly smashed fresh mastodon bones with stone hammers, perhaps to extract marrow or to mine the skeleton for raw materials.

However, many of the world’s leading experts in American archaeology already have expressed some form of skepticism to the paper’s claims. Some have rejected it outright.

“The earliest occupation of the Americas is a highly contentious subject,” says University of Southampton 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.”

Here's everything you need to know about the discovery and the reactions of other archaeology experts.

Where is the mastodon site, and how was it found?

The site was discovered in 1992, when an excavator dug up large bone fragments as California’s State Route 54 was being built through San Diego County.

RELATED: Amazing Animal Migrations by Land, Air, and Sea

The California Department of Transportation requires that paleontologists be on call at major excavations, just in case any fossils pop up amid the carnage. Richard Cerutti, the San Diego Natural History Museum field paleontologist who was on call at the time, flagged the site for follow-up.

He and Deméré then blocked off the area and excavated it, digging down to material undisturbed by the heavy machinery overhead. (Deméré received a grant from the National Geographic Society in January 1993 to support emergency excavations of the site.)

The site struck Deméré as unusual from the beginning, given the large rocks associated with the site, apparent concentrations of bone flakes around the largest stones, and the mastodon remains’ odd arrangement. One of its tusks, for example, was embedded vertically in the dirt.

Wait, the site was found in 1992 and excavated in 1993 ... why is it only being announced now?

The main delay came from the sheer difficulty in accurately dating the site. It wasn’t until 2011 and 2012 that Jim Paces of the U.S. Geological Survey could provide state-of-the-art ages for the mastodon bones, based on the relative amounts of uranium and thorium within them.



Deméré, a paleontologist by training, also had a lot of other projects on his plate. After writing a brief report on the site in 1995 for the California Department of Transportation, he turned his attention to his other research projects, including the evolution of baleen whales.

The first Americans: Clues to an ancient migration

By Nature Video

In the meantime, a small band of online commenters had seized upon his 1995 report as a sign that evidence on the peopling of the Americas was being “suppressed.” Deméré appears surprised and confused by the charge. “Nobody ever said, Forget this ever happened,” he says. “That’s just baloney.”

OK. What’s the new evidence being presented?

To start, the wear features on the rocks match what one would expect from stone tools, specifically those used for smashing up bones, says research team member Richard Fullagar, an archaeologist at Australia’s University of Wollongong.

There’s also the matter of the stones’ placement. The site was entombed in siltstone, a type of sedimentary rock that forms from fine-grained sediments—the sort that would settle out only in very slow-moving, low-energy water. But the large stones that appear to be rudimentary tools are far heavier than the surrounding particles. One is roughly 30 pounds. If water didn’t move the rocks there, then perhaps people carried them to the site.

In addition, fractures on the mastodon bones suggest they were broken while fresh—and the researchers say they couldn’t have been smashed by natural processes. The skeleton likely were not trampled by other large creatures, the team argues, since some of the mastodon’s more fragile bones—such as its ribs and vertebrae—are less shattered than the sturdy limb bones. Nor could smaller animals have done it, the team argues, because scavenging carnivores can’t chew their way through the middle of a fresh mastodon femur.

The team also provided experimental evidence that hammerstones and anvils make similar fracture patterns in fresh elephant bones, suggesting by analogy that such a process could have been at work at the Cerutti site.

Sounds intriguing! Why are other experts so skeptical?

One of the main critiques is that the study doesn’t definitively rule out natural causes for the presence of the purported stone tools, the breakage patterns in the mastodon bones, or the patterns of breakage and wear on their surfaces.

View Images The Cerutti site also revealed unbroken mastodon ribs and vertebrae. Photograph by San Diego Natural History Museum

For one, the paper doesn’t satisfyingly rule out the possibility that natural processes carried the large rocks to the scene, says Vanderbilt University archaeologist Tom Dillehay. Nor does it fully rule out the possibility that the wear patterns on the stones were a result of rocks bumping against one another in a stream, he says.



“When you put the total package together, there’s certainly more evidence to reject [the study] than accept it,” Dillehay says.

It’s not impossible that human history in the Americas is older than currently thought, says Southern Methodist University archaeologist and National Geographic grantee David Meltzer, an expert on early Americans.

“But to prove it, you cannot take broken bones and nondescript stones to make the case, not without demonstrating that nature could not have broken those bones and modified those stones,” he says.

Andy Hemmings, the lead archaeologist at a site of ancient human habitation in Florida called Old Vero, agrees. “We just have to accept that the stones were carried in, [but] from where, and by whom? These are things I’d like to see answered before I’d be willing to put much faith in the conclusions.”

Are there any other concerns about the tools?

Archaeologists also take issue with the stone tools that aren’t there. Usually, hammer-and-anvil sites also come with lithics, flaked stone tools and the debris from their manufacture and use, notes Jim Adovasio, the Florida Atlantic University archaeologist who excavated Meadowcroft Rockshelter, one of North America’s oldest archaeological sites.

These types of tools are missing entirely from the Cerutti site, even though it supposedly dates to a time when hominins were perfectly capable of making sophisticated hand axes.

“They make a statement that the [evidence at Cerutti] is consistent with many other sites,” says Adovasio. “Well, I’m sorry, it’s not—that just isn’t simply true.”

Steve Holen of the Center for American Paleolithic Research, one of the research team’s archaeologists, rebuts the charge, saying that there’s evidence for archaeological sites in the Americas that don’t have flaked stone tools. For the last 25 years, Holen has studied two sites in Kansas and Nebraska that are about 14,000 to 33,000 years old. He claims these sites are also bone quarries where humans did not use flaked stone tools, much like the Cerutti site.

Hemmings however, isn’t convinced that the evidence uniformly supports the idea that humans at Cerutti were trying to use the mastodon bones as tools. In particular, one of the mastodon’s teeth is shattered for no obvious reason.

View Images San Diego Natural History Museum paleontologist Don Swanson points at a rock fragment near a large mastodon tusk fragment. Photograph by San Diego Natural History Museum

“Everything that’s broken was still there, so it wasn’t mined for tools, and you’re certainly not getting marrow out of the bone of a mastodon tooth,” he says. “So what exactly is supposed to have gone on?”

If the stones are tools, though, does that cinch the case for humans?

Not necessarily. The human line doesn’t have a monopoly on tool use, after all. For at least 4,000 years, chimpanzees in Côte d'Ivoire have been cracking nuts with stone hammers. And in Brazil, bearded capuchin monkeys have smashed cashews with rocks for at least a hundred generations.

However, the fossil record of the Americas lacks a marrow-munching, non-human primate at 130,000 years ago. One of the site’s rocks is also nearly 30 pounds—far heavier than the rocks Brazil’s capuchins wield. In addition, “capuchins are too small to generate the kinetic force needed to crack a mastodon bone,” says the University of Georgia’s Dorothy Fragaszy, a National Geographic Explorer who studies capuchin tool use. “I agree with the authors that, if these are hammer stones, humans used them.”

Michael Haslam, an Oxford archaeologist who studies tool use in non-human primates, agrees. “I think that the evidence presented in this paper backs up the authors’ claim that a mastodon has been broken apart using stone tools,” he says. “Overall, I think that we need to consider humans as the starting hypothesis for this site, and go from there.”

Well, that sounds more promising! So if the authors are right, is it possible I’m related to these ancient mastodon miners?

Maybe, although even if the interpretation holds up, it’s unlikely that the tool bearers were anatomically modern humans. At present, there’s no evidence that Homo sapiens sapiens left Africa earlier than 120,000 years ago. But at least four sister species were living in East Asia around the time, and three would be contenders for crossing into the Americas. (The fourth is Homo floresiensis, the much-ballyhooed “hobbits” of Indonesia’s island of Flores—but they’re probably not involved.)

Might the tool users have been Homo erectus, our direct ancestors and the earliest known fire-starters? What about Homo neanderthalensis, which had made it to present-day Kazakhstan around the time of the activity at Cerutti? Or could they have been the Denisovans, the enigmatic East Asian group known from DNA samples collected in a single Russian cave?

At present, it’s impossible to say.

How would any of these species have made the crossing?

The answers vary, since the span of possible ages for the site—120,000 to 140,000 years ago—cover the beginning of the last interglacial, the warm period before the last ice age.

If the site is 140,000 years old, then it’s possible that any tool-wielding hominins could have come to the Americas via Beringia, the land bridge that once connected Siberia and Alaska, says McNabb. But if it’s 120,000 years old—well into the last interglacial—then sea levels would have been much higher. Any would-be migrants would be facing a sea crossing at least 50 miles long.

By 130,000 years ago, hominins undoubtedly figured out how to cross open water. A site in Crete called Mochlos bears stone tools that could be about 130,000 years old, but Crete was never connected to the Greek mainland by a land bridge.

But at present, there’s no solid evidence that hominins had made it into northeastern Siberia before about 30,000 years ago—much less any evidence that they floated across the Bering Strait a hundred thousand years before that.

View Images A close-up view of a spirally fractured mastodon femur bone from the site. Photograph by Tom Deméré, San Diego Natural History Museum

“I think a sea crossing to the Americas with a much higher sea level is a much more difficult proposition,” says McNabb.

Have claims for sites this early been made before?

For the most part, American archaeology has been caught in a bitter debate over whether humans arrived a couple thousand years earlier than previously thought—not a hundred thousand years before.

“The earliest occupation of the Americas is a highly contentious subject,” says McNabb.

For decades, convention had held that around 13,000 years ago, an ice-free corridor opened up from Alaska to Montana, providing passage to a group of humans who had trekked across Beringia. Within 500 years, these migrants were thought to have successfully peopled the Americas—leaving behind a type of fluted stone point that became a calling card of sort for the Clovis culture.



But beginning in the 1970s, archaeologists—including Adovasio and Dillehay—began to find evidence of sites that predated the Clovis culture, such as Pennsylvania’s Meadowcroft Rockshelter and Chile’s Monte Verde, excavations that the National Geographic Society helped fund.

A brutal—and sometimes deeply personal—debate over the legitimacy of these “pre-Clovis” sites ensued. In the case of Monte Verde, it took Dillehay nearly two decades to convince many of his peers that the site predates the Clovis culture. Some Clovis-first holdouts still don’t buy it.

Dramatically extending the timeline for humans in the Americas makes the Cerutti claim even more contentious. And few previous claims of sites this much older have survived the academic wringer.

In the 1960s, for instance, famed archaeologist Louis Leakey received several National Geographic Society grants to fund excavations at Calico Hills, a site in California that had been rumored to contain stone tools at least a hundred thousand years old.

Unfortunately for Leakey, the site’s particular geology produced stone flakes that looked a lot like tools—making it all but impossible to tell the difference between natural and human-made objects. Modern consensus is that the stone “tools” are naturally occurring.

“Nobody’s gone back and seriously touched that site at all,” says Dillehay. “Leakey was burned, [and] the people associated with the site were burned, so to speak. These things happen.”

Can the researchers do anything else to back up their claim?

Yes. Deméré and his colleagues are currently examining the stone tools from the site for protein residues. If they really were used to smash the mastodon bone, microscopic bits of mastodon likely would have been ground into the rocks’ nooks and crannies.

The researchers also say they’re interested in re-excavating the site, part of which remains in an earthen dam in San Diego County intended to dull the noise from California’s State Route 54. In the meantime, the authors say that they’re prepared to defend their analysis from the years, if not decades, of fierce criticism ahead of it.

“I think we’ve made a very good case that this is an archaeological site,” says Holen. “I think we’re quite prepared for the firestorm that’s coming.”</s>Nature

San Diego Natural History Museum

San Diego Natural History Museum

San Diego Natural History Museum

Tom Deméré, San Diego Natural History Museum

Tom Deméré, San Diego Natural History Museum

Tom Deméré, San Diego Natural History Museum

San Diego Natural History Museum

San Diego Natural History Museum

Kate Johnson, San Diego Natural History Museum

In 1992, a group of archaeologists found something extraordinary buried below a sound berm next to the San Diego freeway in Southern California. They had been called in during a freeway renovation to do some excavation because the fossil-laced earth of the California coast often yields scientific treasures. After digging about three meters below the construction area, Center for American Paleolithic Research archaeologist Steve Holen was deep into a pristine layer of soil that hadn't been disturbed for millennia. There, he found what appeared to be an abandoned campsite, where humans had left stone tools and hammered mastodon bones behind. This wasn't too unusual; it's fairly well-established that humans were hunting mastodons in the Americas as early as 15,000 years ago.

Evidence and skepticism

But when Holen's colleagues used several techniques to discover the age of the bones, the numbers sounded crazy. Test after test showed that the bones had been buried more than 100,000 years ago. The result flew in the face of everything we think we know about the spread of humanity across the globe. It took 24 years before Holen and his fellow researchers were certain enough to publish their findings in Nature . Now, based on a reliable dating method using Uranium decay rates and years of repeated tests, the researchers say that an unknown type of early human lived in California roughly 130,000 years ago. If true, it completely changes the story of how humans reached the Americas.

What the researchers found at the site, dubbed Cerutti Mastodon, looks very much like a perfectly preserved tableau of an ancient tool-making workshop. Stone "anvils," or flat rocks, are surrounded by a scattering of smaller "cobbles" used as hammers. Mixed in with these items are shattered mastodon bones and teeth, many of them crushed in a way that could only be done by a human with a stone tool. It's clear that the stones were deliberately struck against each other because there are stone flakes that perfectly fit into the cobble hammers, possibly broken off while the bones were being worked. The breaks and scoring marks on the bones suggest that people were breaking them open to get at the marrow, as well as crafting them into tools. Some of the mastodon bones, like the tusks, were left untouched. Holen and his colleagues argue that if these bones had been disturbed by animals or some kind of natural disaster, they would all have been damaged in the same way. But that's not what we see.

"People were breaking up the limb bones of a mastodon, removing some of the big, thick pieces," Holen said at a press conference. "They were extracting marrow for food. And they were using old technology. We have evidence of people in Africa 1.5 million years ago breaking up elephant limb bones with this same [stone] technology." Another author on the paper, University of Wollongong archaeologist Richard Fullagar, is an expert on the kinds of microdamage that humans leave behind on stone tools. "The evidence at this site is remarkable," he said. When he first identified stone tools from the site, he didn't know their age. "They were pounding stones. All the materials indicated that they had been used for smashing up bones. You can see fragments of hammers and anvils that can be fitted back into the stones... It's rare that you get all that evidence at one site. It really does show humans have been there."

Just to make sure these kinds of stone tools could damage mastodon bones in the way they found them at Cerutti Mastodon, Holen and his colleagues conducted several experiments. They built stone-age tools and smashed elephant bones. After several such experiments, it was clear that one of the only ways to produce the damage they saw on those 130,000-year-old mastodon limbs was to crush them with rock cobbles on rock anvils.

Current data suggests Homo sapiens spread out of Africa around 100,000 years ago, across Asia about 60,000 years ago, into Europe and Australia 50,000 years ago, and finally the Pacific coasts of both North and South America, and probably interior continental locations by 13,500 to 15,000 years ago. To confirm the presence of an undefined species of Homo in the Americas at 130,000 years ago requires indisputable evidence. While the Cerutti Mastodon site challenges our knowledge of the peopling of America and forces us to think beyond what is currently known, fresh fractured bone together with five large cobbles is not extraordinary evidence.

Reactions to the paper in the scientific community are veering between skepticism and shock. Some say the Cerutti Mastodon site may have been too disturbed by freeway construction to be trustworthy. Others say it's clear that the site is undisturbed, but we still can't be sure that the evidence found by Holen and his colleagues is enough. Trent University archaeologist Daniel Rafuse , who has worked on some of the most ancient human sites found in Argentina, quoted Carl Sagan's famous line, "extraordinary claims require extraordinary evidence." Speaking via e-mail to Ars, he continued:

University of Wisconsin, Madison paleoanthropologist John Hawks was flummoxed. He told Ars, "I’m not usually at a loss for words, but this one has left me and many of my friends speechless."

Some scientists were absolutely convinced, however. Berkeley Geochronology Center geologist Warren Sharp, who is an expert in the kind of Uranium dating used to verify the age of the mastodon bones, praised the careful work the researchers had done. "The samples they used are some of the actual broken bones, so the samples and the context are clear," he told Ars by phone. He explained that Uranium dating measures the decay of the element after it has been taken up by bones from minute amounts of water in the soil. Because Uranium is very mobile, seeping into and out of porous objects like bone, the test can sometimes result in artificially old ages. But after examining the researchers' work in this paper, Sharp was satisfied that they had accounted for this potential problem by dating three different samples, taking multiple samples from each bone. This technique corrects for the problems caused by Uranium's mobility. "This is a reliable approach and it’s been done with care by people who have analyzed standards and ensured quality of the data," he concluded.

Holen, who first discovered the 130,000 year-old Cerutti Mastodon site, said he was prepared for the skepticism. At a press conference, he said that he and his colleagues had found other sites dating back to 30,000 years ago in the American Great Plains. Though these findings were controversial, he sees this new discovery as validating a new version of history where human ancestors were in the Americas long before most modern Homo sapiens had made it out of Africa.

Who were these mystery humans?

Currently, scientists believe that several different waves of humans came to the Americas from Asia between 12,000-20,000 years ago. Some nosed their way along the rich coastal ecosystems in boats, possibly walking part of the way through Beringia or the Bering Land Bridge. Some may have walked most of the way after the planet warmed and ice sheets covering most of Canada and the northern US withdrew. The Cerutti Mastodon discovery, say the researchers, doesn't change that story. It just adds a new wave of human explorers who came over 100,000 years earlier.

The timing makes sense, at least in terms of climate. About 130,000 years ago, the planet went through a warm, interglacial period when the coastal route would have been relatively ice-free, allowing people to find food as they gradually made their way from Asia to the Americas. It's even possible that Beringia would have been as walkable as it was in the late Pleistocene.

But who were these humans who made it all the way to the Americas and turned a mastodon into bone tools? That's what paleoanthropologist Hawks is wondering, too:

The key question is, which hominin population had the ability to establish a sustained population in Beringia? We don’t even know how many populations were in mainland Asia at the time—certainly multiple, deeply divergent populations of Denisovans and Neanderthals, maybe others with even older origins. Maybe modern humans. From the biological side, we have no reason to think that any of them were incapable of entering the New World. We’ve just been stuck with the assumption that they didn’t cross into North America—because if they did, we should see a hundred millennia of discarded tools and butchered animal bones.

Holen and his colleagues essentially agree with Hawks' point. In their paper, they suggest that the humans whose tools they found in California might have been Neanderthals or Denisovans. Probably, they conceded, these humans were a hybrid of several early humans, and possibly even a form of early Homo sapiens who roamed Asia more than 200,000 years ago. There is also evidence that humans in Indonesia had boats over 180,000 years ago, because there are human remains from that time on Indonesian islands that could not have been reached any other way. So we have humans and boat technology in Asia. And we have a climate that would allow for their passage to the Americas.

If we accept all this evidence, the question remains: what happened to those early Americans, and why haven't we seen more of their discarded stones and bones? Holen believes that these early mastodon hunters probably lived in very dispersed, small bands. The population was low. Plus, he noted, "It’s possible that the early population came in and did not make it. Humans could become locally extinct if the environment wasn't favorable for human adaptation in that area." So we may not ever find many of these people's tools because there were so few of them, or they simply died out before leaving much behind.

Still, while they were alive, they enjoyed a good life on the California coast, says San Diego Natural History Museum paleontologist Thomas Deméré, who worked on the paper with Holen. 130,000 years ago, he said, the Cerutti Mastodon site "was a meandering stream close to sea level. It was occupied by ice age mammals including camels, horses, ground sloths, dire wolves, deer, and capybara. It was very nice I would think, not far from the coastline." As scientists gather more evidence and search for more signs of these ancient Americans, we're left with a startling new vista on an alternate history that might just turn out to be our own.

Nature, 2017. DOI: 10.1038/nature22065

Listing image by San Diego Natural History Museum</s>A hominid species may have lived in what is now California as long as 130,000 years ago — turning the record of early humans in North America upside down, according to a provocative paper published Wednesday in the journal Nature.

Scientists say an archaeological site in San Diego County shows tell-tale evidence of human behavior: specifically, bones and teeth of an elephant-like mastodon that appear to have been smashed with rocks. Uranium-thorium dating puts the bones at 130,000 years old, researchers said.

“What makes sense to us, even though it’s out there, is the hypothesis that humans brought these rocks to the site, and that humans used these rocks to break bone,” lead researcher and paleontologist Thomas Deméré of the San Diego Natural History Museum said in a statement.

Combining insights from paleontology and archaeology, Deméré and his team believe that early humans used this site to break up mastodon bones.

“The bones and several teeth show clear signs of having been deliberately broken by humans with manual dexterity and experiential knowledge,” Dr. Steve Holen, director of research at the Center for American Paleolithic Research, said in a statement.

The team found no traces of human remain at the site.

If confirmed, the new signs of human activity would be 100,000 years earlier than the “broadly accepted date for the first occupation of the Americas,” said researcher John McNabb of the University of Southhampton.

“The CM (Cerutti Mastodon) site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas,” researchers wrote.

The first Americans: Clues to an ancient migration by on YouTube

The southern California site was first discovered during routine construction work to expand a freeway in 1992. Brought in to excavate, paleontologists found hammerstones, stone anvils, and the skeleton of a single mastodon. They placed the site within the early late Pleistocene epoch, but struggled to put a precise date on it at the time.

Now, the researchers are calling for further archaeological investigation to help expand our knowledge of the earliest human presence on the continent.

“Until we find a skeleton, at this site or at a site of a comparable age in the Americas, it’s all open to speculation, and we just don’t know,” McNabb said.</s>In the winter of 1992, a construction crew in San Diego, California started cutting into the rocks that flanked the State 54 Highway, in a bid to widen the road. Those rocks hailed from the Pleistocene period and were rich in Ice Age fossils, so scientists from the San Diego Museum of Natural History accompanied the crew to recover whatever they unearthed. Among bits of horse, camel, dire wolf, and ground sloth, they found the remains of a single mastodon—an extinct mammoth-like animal. “And we noticed there was something different about it,” says Thomas Deméré, who was part of the team. Based on several lines of evidence—the way the bones are broken, the way they lay, the presence of large stones that show curious patterns of wear and are out-of-place in the surrounding sediment—the team think that early humans used rocks to hammer their way into the mastodon’s bones. That wouldn’t have been contentious in itself, but the team also claims that the bones from the “Cerruti Mastodon” are 130,000 years old. That would push back the earliest archaeological evidence for humans in North America by a whopping 115,000 years.

To put that in perspective, for decades, the first American settlers were thought to be the Clovis people, who arrived 13,000 years ago. But by discovering older sites with strong evidence of human activity, archaeologists confirmed that the continent had a pre-Clovis presence that dates back 14,600 years—or perhaps even further. Genetic studies have also suggested that modern humans entered America from Asia even earlier, around 23,000 years ago. Each of these claims was a bold one. “We archaeologists had a tough-enough time accepting that there are sites in the Americas greater than 13,000 years old—and a few of us still haven’t accepted that,” says Bonnie Pitblado from the University of Oklahoma. “But 130,000 years—ten times that far back in prehistory? That’s an enormous leap for a profession that, for all its focus on changes in human culture through time, really does not like to change its views.” “If the authors are correct, it would completely rewrite our best understanding of the peopling of the Americas,” says Jon Erlandson from the University of Oregon. “As scientists we're supposed to keep an open mind, but I doubt that many archaeologists will be convinced by this case. Extraordinary claims require extraordinary evidence, and I didn't find it here.” David Meltzer from Southern Methodist University concurs. “If you are going to push human antiquity in the New World back more than 100,000 years in one fell swoop, you’ll have to do so with a far better archaeological case than this one,” he says.

Most of the experts I spoke to weren’t convinced by the presented evidence, and some were downright disdainful. “I was astonished, not because it is so good but because it is so bad,” says Donald Grayson from the University of Washington. But not everyone is ready to dismiss the study yet. “This paper is a fantastic hypothesis,” says Zeray Alemseged from the University of Chicago. If the team is right, the perpetrators who broke the mastodon couldn’t possibly have been Homo sapiens, since our species hadn’t left Africa 130,000 years ago. But at the time, the planet was full of other hominids, including Homo Erectus, Neanderthals, Denisovans, and the “hobbits” of Flores. “Could it be that some of them ventured into North America, back then? Why not? Could there have been another species of Homo hanging out in California? Knowing how migratory our genus is I wouldn’t be surprised.” “I think they’ve have made a very strong case,” says Pitblado. “They presented compelling evidence that doesn’t make this site a slam dunk, but must be taken seriously. I predict that most archaeologists will roll their eyes. What they’re unlikely to do is give the site a chance.” 

 A schematic of the Cerruit mastodon, showing recovered bones and teeth. Dan Fisher & Adam Rountrey, University of Michigan. Since 1993, the team, including lead author Steven Holen, have repeatedly tried to date the mastodon fragments, using techniques like carbon-dating. They repeatedly failed. They only succeeded when they turned to uranium-thorium dating, which looks at the decay of two radioactive elements. That gave an age of 130,700 years, give or take 9,400 in either direction. None of the people I contacted raised issues with those dates, but the team’s other clues are more controversial.

They found the mastodon’s bones in a couple of concentrated clusters rather than in a scattered mess. The tops of both thigh-bones had broken off and were lying side-by-side, amid a concentration of other bones. One of the tusks was lying horizontally in the sediment, the other was sticking up vertically. The team think that the remains of a naturally decaying mastodon wouldn’t have ended up in such distinctive patterns—and the bones of nearby bones of wolves and horses certainly didn’t. And although fragile bones like ribs and vertebrae were still intact, stronger ones like molars and thigh-bones were broken. The fractures aren’t consistent with chewing teeth or trampling feet; instead they look like the breaks you get when you deliberately smash a still-living bone. The team even tried doing this: they smacked modern elephant and cow bones with rocks, and got fractures very similar to the ones on the Cerruti mastodon. At the site, the team found five large stones (cobbles) amid their clusters of bones, which could have acted as hammers and anvils. These rocks sat in a layer of fine, silt-like sediment, and were far bigger and harder than anything around them. “How did they get there?” says Deméré. “They weren’t being transported by flowing water at the same time as the silt.” Instead, he suggests that they were carried to the site and used to infiltrate the mastodon bones—presumably to get at the marrow within. Sure enough, the rocks showed signs of impact, and the team even managed to fit several detached flakes back onto the “parent” stones.

Could these patterns have been caused by anything else? Could the bones have been trampled by heavy feet, chewed or crunched by scavengers, or displaced and eroded by water? “I cannot envision another scenario than human involvement that introduces heavy mastodon bones, lighter mastodon bones, and heavy cobbles into an otherwise well-sorted, fine-grained matrix,” says Pitblado. And Deméré adds that his team took care to rule out alternative explanations. “It’s the totality of the site—all these different lines of evidence that can’t be explained by processes other than human activity,” he says. But “nature is mischievous and can break bones and modify stones in a myriad of ways,” says Meltzer, who thinks that the evidence is “inherently ambiguous.” Ariane Burke from the University of Montreal adds that the fractures are consistent with the bones having been struck by a heavy object while still fresh—but it’s not clear if humans did the striking. The problem is that in focusing on the fractures, the team haven’t published information on the rest of the bones, which might reveal signs of weathering or other natural abrasions. “It is one thing to show that broken bones and modified rocks could have been produced by people, which they’ve done,” says Grayson. “It is quite another to show that people, and people alone, could have produced those modifications. This they have most certainly not done, making this a very easy claim to dismiss.”

Even if Holen, Deméré, and their colleagues are right, why has no one else found any trace of these bone-smashing pioneers? “Where are the clearly recognizable artifacts that hominins throughout the Old World were making 130,000 years ago?” says Erlandson. “And if people were in California at this time, what happened to them for the next 100,000 years?” Deméré can only speculate. Perhaps these people represented a failed attempt to colonize the New World—they arrived but eventually disappeared, leaving a hominid-less window of time before others entered America much later. And “maybe archaeologists just aren’t looking in 130,000-year-old rocks for evidence of humans,” he says. “You have to ask the question first. Maybe sites like this have been found but haven’t been recognized for what they are.” But “it’s unlikely that archaeologists have missed these sites, as people have been looking for Pre-Clovis for decades and other paleontological sites for the past century,” says Lauren Norman from Kansas University. And how, she wonders, did these hypothetical pioneers even get to North America? “They would have had to have either go by boat, or travel through the Bering Strait. There is very little evidence for long-distance boating technology at this time. And if people traversed the Bering Strait during a glacial period, they would have had to have Arctic adaptations. The earliest evidence of people using the Arctic is around 40,000 years ago.” “Scientific claims of this magnitude require far more than plausibility.” Controversies like this aren’t new. In the late 70s, researchers suggested that stone artifacts in California’s Calico Hills were 200,000-year-old tools—but others argued that they were likely shaped through natural processes. Another group of Californian artifacts, also recovered near San Diego, were billed as 125,000-year-old grinding stones, and that claim was also discredited for similar reasons. “The North American archaeological literature is full of claims like this,” says Grayson. “There is no reason to think that this new one will receive a different professional reaction.”

When I asked him what level of evidence he would need to be convinced, he admits that the Cerruti team is in a tough situation. “There’s probably a nearly-infinite set of natural processes that could produce damage of this sort and no one could reasonably be expected to eliminate all of them,” he says. “The kinds of damage they illustrate are known to occur in non-archaeological settings, often from unknown processes. This might seem unfair—unknown processes are, by definition, impossible to eliminate—but scientific claims of this magnitude require far more than plausibility.” Michael Waters from Texas A&M University would be more convinced by the presence of “unequivocal stone tools.” Those might include knapped stones used to cut bone and butcher meat. But “If you think of this as an expedient site for processing bone, where you break it and cart it off somewhere else, there’s really no reason for refined tools,” says Deméré. “It’s not a butchery site.” Burke says that she’s like to see them “compare their bone assemblage to those of a similar age, where we know humans were exploiting mammoths in Eurasia.” And Alemseged thinks that it might not be possible to settle the debate unless someone finds fossils of these hypothetical pioneering hominids. “We need bones to really finalize this business,” he says.</s>Scientists say the patterns of breakage in mastodon bones found 25 years ago near a San Diego highway suggest that humans battered the beast 130,000 years ago.

That’s a shocker, because before now, the oldest widely accepted evidence of human habitation in North America goes back only about 16,000 years. If the scientists are right, that makes the place they studied, known as the Cerutti Mastodon site, the oldest archaeological site in North America.

“It’s somewhat mind-boggling to have 130,000 years proposed,” said University of Oregon archaeologist Dennis Jenkins. He has found previous evidence for human habitation in 14,000-year-old preserved poop but wasn’t involved in the latest study, published today by the journal Nature.

The researchers behind the newly reported find came upon their evidence way back in 1992, when they made a routine check of a construction site for a noise-reducing berm near State Route 54 in San Diego. The site was promising enough for the scientists to dig 10 feet below the level of the construction crew’s excavation.

What they found was intriguing: Bones, tusks and molars from a mastodon were buried alongside large stones that appeared to have been used as hammers and anvils for breaking up the bones. That posed a puzzle: Apparently, humans were in what is now Southern California long before they were supposed to be.

The site would have been close to sea level back then, with a meandering stream running through it, said study co-author Tom Deméré, curator of paleontology and director of PaleoServices at the San Diego Natural History Museum. “A very nice place to live, I’d think, 130,000 years ago,” he told reporters.

But the researchers knew they had to be sure about what they thought they were seeing. “Of course, extraordinary claims like this require extraordinary evidence,” Deméré said.

Over the years that followed, researchers painstakingly put the puzzle pieces together. They studied how the break marks on bones and the chip marks on stones, and concluded all those marks could only have resulted from tools being used intentionally.

To test their hypothesis, they even beat away at bones from dead elephants, including a leg bone from Tanzania and a carcass that had been buried in Colorado three years earlier.

“The bone was extremely fresh, and smelled very bad. I almost wished that I never continued that experiment when we dug it up. But we did,” said lead author Steve Holen, director of research at the Center for American Paleolithic Research. Holen and his strong-armed colleagues produced similar patterns of breakage and chipping, using stone hammers modeled after the ones that were found at the construction site.

Uranium-thorium dating of bone samples indicated that the mastodon was 130,000 years old, with a conservative margin of error of plus or minus 9,400 years.

“It’s hard to argue with the clear and remarkable evidence,” said co-author Richard Fullagar, an archaeologist at the University of Wollongong in Australia.

Nevertheless, there are arguments. Skeptics wonder whether the site may have been disturbed, or whether the dating estimates could be off. Also, the bones showed no evidence of the cut marks typically associated with butchering.

The researchers insist that there are no signs the site had been disturbed at the depths they excavated, that the dating estimate is as solid as it can be. They surmise that the hunters may have been after the marrow inside the bones.

“It’s not so much to do with the dating – that seems to be the standard kind of stuff that’s been applied in Africa,” he told GeekWire. “It’s the fact that they have this huge gap between what’s accepted and what they’re claiming. … Where have these people been?”

The researchers speculate that these people may have been ancient Asians, perhaps Neanderthals or Denisovans, who figured out a way to get to North America. They may have walked from Siberia and Alaska, over a land bridge that disappeared about 135,000 years ago. Or they may have sailed around the coasts of Asia and North America to land in California.

The early humans may have died out, leaving little trace of human existence until a fresh wave of immigrants swept in more than 100,000 years later. Such scenarios are mere speculation, however, because no human remains were found at the Cerutti Mastodon site.</s>NEW YORK (AP) — A startling new report asserts that the first known Americans arrived much, much earlier than scientists thought — more than 100,000 years ago __ and maybe they were Neanderthals.

If true, the finding would far surpass the widely accepted date of about 15,000 years ago.

Researchers say a site in Southern California shows evidence of humanlike behavior from about 130,000 years ago, when bones and teeth of an elephantlike mastodon were evidently smashed with rocks.

The earlier date means the bone-smashers were not necessarily members of our own species, Homo sapiens. The researchers speculate that these early Californians could have instead been species known only from fossils in Europe, Africa and Asia: Neanderthals, a little-known group called Denisovans, or another human forerunner named Homo erectus.

“The very honest answer is, we don’t know,” said Steven Holen, lead author of the paper and director of the nonprofit Center for American Paleolithic Research in Hot Springs, South Dakota. No remains of any individuals were found.

Whoever they were, they could have arrived by land or sea. They might have come from Asia via the Beringea land bridge that used to connect Siberia to Alaska, or maybe come across by watercraft along the Beringea coast or across open water to North America, before turning southward to California, Holen said in a telephone interview.

Holen and others present their evidence in a paper released Wednesday by the journal Nature . Not surprisingly, the report was met by skepticism from other experts who don’t think there is enough proof.

The research dates back to the winter of 1992-3. The site was unearthed during a routine dig by researchers during a freeway expansion project in San Diego. Analysis of the find was delayed to assemble the right expertise, said Tom Demere, curator of paleontology at the San Diego Natural History Museum, another author of the paper.

The Nature analysis focuses on remains from a single mastodon, and five stones found nearby. The mastodon’s bones and teeth were evidently placed on two stones used as anvils and smashed with three stone hammers, to get at nutritious marrow and create raw material for tools.

Patterns of damage on the limb bones looked like what happened in experiments when elephant bones were smashed with rocks. And the bones and stones were found in two areas, each roughly centered on what’s thought to be an anvil.

The stones measured about 8 inches (20 centimeters) to 12 inches (30 centimeters) long and weighed up to 32 pounds (14.5 kilograms). They weren’t hand-crafted tools, Demere said. The users evidently found them and brought them to the site.

The excavation also found a mastodon tusk in a vertical position, extending down into older layers, which may indicate it had been jammed into the ground as a marker or to create a platform, Demere said.

The fate of the visitors is not clear. Maybe they died out without leaving any descendants, he said.

Experts not connected with the study provided a range of reactions.

“If the results stand up to further scrutiny, this does indeed change everything we thought we knew,” said Chris Stringer of the Natural History Museum in London. Neanderthals and Denisovans are the most likely identities of the visitors, he said. Denisovans, more closely related to Neanderthals than to us, are known from fossils found in a Siberian cave.

But “many of us will want to see supporting evidence of this ancient occupation from other sites, before we abandon the conventional model of a first arrival by modern humans within the last 15,000 years,” he wrote in an email.

Erella Hovers of the Hebrew University of Jerusalem and the Institute of Human Origins at Arizona State University in Tempe, who wrote a commentary accompanying the work, said in an email that the archaeological interpretation seemed convincing. Some other experts said the age estimate appears sound.

But some were skeptical that the rocks were really used as tools. Vance Holliday of the University of Arizona in Tucson said the paper shows the bones could have been broken the way the authors assert, but they haven’t demonstrated that’s the only way.

Richard Potts of the Smithsonian Institution’s National Museum of Natural History, said he doesn’t reject the paper’s claims outright, but he finds the evidence “not yet solid.” For one thing, the dig turned up no basic stone cutting tools or evidence of butchery or the use of fire, as one might expect from Homo sapiens or our close evolutionary relatives.

The lead author, Holen, told reporters Tuesday that he and co-authors were ready for such criticism.

“We expected skepticism because of the extremely old age of this site,” he said. “I think we made a very good case.”</s>Who were the first Americans?

Their contention, if correct, would force a dramatic rethink of when and how the Americas were first settled — and who by. Most scientists subscribe to the view that Homo sapiens arrived in North America less than 20,000 years ago . The latest study raises the possibility that another hominin species, such as Neanderthals or a group known as Denisovans , somehow made it from Asia to North America before that and flourished."It's such an amazing find and — if it's genuine — it's a game-changer. It really does shift the ground completely," says John McNabb, a Palaeolithic archaeologist at the University of Southampton, UK. "I suspect there will be a lot of reaction to the paper, and most of it is not going to be acceptance."The study focuses on ancient animal-bone fragments found in 1992 during road repairs in suburban San Diego. The find halted construction, and palaeontologist Tom Deméré of the San Diego Natural History Museum led a five-month excavation. His crew uncovered teeth, tusks and bones of an extinct relative of elephants called a mastodon (Mammut americanum), alongside large broken and worn rocks. The material was buried in fine silt left by flowing water, but Deméré felt the rocks were too large to have been carried by the stream."We thought of some possible explanations for this pattern, and the process we kept coming back to was that humans might be involved," he says. Attempts in the 1990s to date the site suggested that the ivory was some 300,000 years old, but Deméré was sceptical: the method his colleagues used was problematic, and the age seemed so improbable for humans to be living in California.Over the past decade, archaeological research and studies of modern and ancient DNA have reached a consensus view on the peopling of the Americas : humans from Asia crossed the Bering land bridge into Alaska some 20,000 years ago and reached the southern tip of South America around 14,000 - 15,000 years agoSome archaeologists, however, maintain that humans arrived earlier. They point to sites containing rocks that resemble stone tools as well as large animal bones that have damage apparently inflicted by humans. Deméré's co-authors Kathleen Holen and her husband Steven Holen, archaeologists at the Center for American Paleolithic Research in Hot Springs, South Dakota, have put forward several sites in the US Midwest as evidence for a human presence in the Americas up to 40,000 years ago. But many scientists have viewed these claims with scepticism.After hearing about the San Diego mastodon, the Holens visited Deméré in 2008 to see the boxed-up remains. "We were looking at something very, very old, but it had the same fracture patterns that we had seen before," says Kathleen Holen. The bones looked as though they had been set on by a large 'anvil' stone and struck with a 'hammer' rock. The team contends that the rocks recovered from the site were used either to extract the mastodon's bone marrow or for making more-delicate bone tools. There are no obvious cut marks on the mastodon bone, suggesting that the animal wasn't killed or butchered for its meat.Using refined dating methods, the researchers tried again to determine the age of the site. They couldn't use radiocarbon dating on the mastodon remains because the bones lacked carbon-containing collagen protein. A second method was too imprecise. A third technique, which measures relative levels of radioactive uranium and thorium in bone, suggested that the remains are 130,000 years old. "I'm sure that many of our colleagues are going to be quite sceptical. I would expect that. This is far, far older than most archaeologists expect hominins to be in North America," says Steven Holen. "I say that even for myself."Alistair Pike, an archaeological scientist at the University of Southampton who specializes in uranium dating, notes that the team's method relies on simplified models of how uranium seeps from groundwater into bone, but he sees no obvious flaws in the dating work. "At face value, these results are about as good as it can get," he says.Collecting ancient DNA from the remains and determining the animal's evolutionary relationship to other mastodons could also help to establish the site's age, notes Pontus Skoglund, a population geneticist at Harvard Medical School in Boston, Massachusetts, who works on ancient DNA. If the discovery holds up, he adds, "it would be one of the most Earth-shattering revisions of our view of the peopling of the world".Before invoking humans, however, the researchers need to better rule out the possibility that natural forces broke the rocks and bones, says David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas. "If you are going to push human antiquity in the New World back more than 100,000 years in one fell swoop, you'll have to do so with a far better archaeological case than this one."McNabb would like to see the breakage patterns analysed in more detail. He finds it "curious" that the site yielded no other traces of human presence, such as the shaped stone tools that are typically found at much older animal-butchery sites in Africa.Erella Hovers, an archaeologist at the Hebrew University of Jerusalem who reviewed the paper for Nature, says she raised her eyebrows when the manuscript arrived in her inbox: "I was like, 'Uh, really?'" But after revisions that elaborated on the dating work and demonstrated that hitting modern elephant bones with large rocks produces damage patterns similar to those seen on the mastodon bones, Hovers is now convinced that hominins created the California site. "This is mind-boggling," she says. "It leaves a ton of questions because we know nothing else, except that there were some sort of people there at this time."If humans or their ancient relatives were responsible, there are several candidates. The ancestors of modern non-African humans left the continent less than 100,000 years ago , but earlier migrations out of Africa might have reached North America, Deméré and his co-authors say. They point to 100,000-year-old Homo sapiens-like teeth from China and to hints that some indigenous groups in South America carry trace ancestry from a possible earlier migration into the Americas Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, favours Denisovans or Neanderthals, which both lived in southern Siberia at least 100,000 years ago. Yet there is no evidence that either group could survive the epic Arctic voyage across from Siberia to Alaska. "Many of us will want to see supporting evidence of this ancient occupation from other sites before we abandon the conventional model of a first arrival by modern humans within the last 15,000 years," Stringer says."We're going to start looking," says Deméré, who has his eye on another California site that his team excavated a few years ago.Steven Holen hopes that other scientists will join the search. "Keep your eyes open for this kind of material when you're out in the field," he says. "Don't just say 'This can't be'."</s>I’ll just put this up here without analysis, as I haven’t yet read the paper. But it’s big news if true. A new a new report Nature by Holen et al. (reference below; free access) claims to have found human tools associated with crushed and cracked mastodon bones at a site in southern California, with the date a full 130,000 years ago!

Conventional wisdom puts the arrival of humans in North America about 15,000-20,000 years ago, coming from Siberia across the Bering Strait. These hominins are nearly ten times older, and well older than those individuals who left Africa about 60.000 years ago to colonize the globe.

Who were these hominins? Were they a species that went extinct? Or is it a mistake? If this is true, it’s a remarkable and game-changing discovery. Have a look at the paper.

And here are some of the tools:

Holen, S. R., T. A. Deméré, D. C. Fisher, R. Fullagar, J. B. Paces, G. T. Jefferson, J. M. Beeton, R. A. Cerutti, A. N. Rountrey, L. Vescera, and K. A. Holen. 2017. A 130,000-year-old archaeological site in southern California, USA. Nature 544:479-483.</s>Ancient remains found in California suggest that humans were present in North America some 130,000 years ago — substantially earlier than scientists previously thought.

A site in San Diego contains evidence that early human ancestors smashed mastodon bones and teeth to make rudimentary tools. The smattering of bone fragments, hammer-stones, and anvils now represents the oldest archeological site in the Americas, according to a study published in the journal Nature on Wednesday.

The oldest widely accepted date for humanity's presence in North America is less than 15,000 years ago. If the findings are true, this would make the San Diego site older by a factor of nearly ten, the study found.

SEE ALSO: A 400,000-year-old fossil offers new clues on how humans evolved

"Extraordinary claims like this require extraordinary evidence, and we feel that the Cerutti Mastodon site [in San Diego] preserves such evidence," said Thomas Deméré, the study's corresponding author and curator of paleontology at the San Diego Natural History Museum.

Some outside experts said they were deeply skeptical that the site is as old as the scientists claim, or that the mastodon bones show definitive signs of human activity.

"I was astonished, not because it is so good but because it is so bad," Donald Grayson, an archaeologist at the University of Washington, told the New York Times. He faulted the study for failing to rule out other explanations for markings on the bones.

John McNabb, an archeologist at the University of Southampton in England, said the study raises more questions than answers. In a commentary published in Nature, he said that, to prove this is truly evidence of human activity, more information is needed about how people even arrived there so long ago.

But archeologist Erella Hovers agreed the study "points to a much earlier arrival of human relatives" than previous studies suggest.

The new finding "has been rigorously researched and presented," Hovers, a professor at the Hebrew University of Jerusalem, wrote in a commentary for Nature. However, the scientists' proposed narrative about the bone data "has some gaping holes that need filling," she added.

The study's authors said they don't know which kind of early human ancestor was responsible for the bone breaking, since no human remains were found at the site. They also don't know how humans arrived in southern California, though they might've crossed the Bering Strait or traveled in a water craft from Asia.

Deméré and his colleagues acknowledged the skepticism toward their study. But they defended their results on a Monday call with reporters, noting the study was the result of more than two decades of research. San Diego paleontologists first discovered the mastodon bones and rock tools in 1992, during a routine survey at a freeway construction site. Using an excavator, scientists dug nearly 10 feet below the surface to uncover the remains, which neither geological forces nor human activity had disturbed in over 100,000 years, said Steve Holen, the study's lead author and director of research at the Center for American Paleolithic Research in South Dakota. 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). Deméré said back then, the site likely sat near a meandering stream near the coastline, the landscape filled with extinct Ice Age megafauna, including camels, horses, and deer. Today, the dig site is part of a sound berm on the north side of a San Diego freeway. Mastodon rib bones, vertebrae, and femurs showed distinct fracture lines that suggest they were broken while fresh — not run over by a truck or demolished by nature millennia later. Other bone and molar fragments showed evidence of being hit with hard objects, while five large hammer-stones and anvils at the site show signs of wear and tear that could only come from human interference, scientists said. To verify their findings, the team conducted two experiments on elephant bones using large rock hammers and anvils, and produced the same types of fracture patterns. "People were here breaking up the limb bones of this mastodon ... probably to make tools out of, and they may also have been extracting the marrow for food," Holen said. He noted that human ancestors in Africa used this same approach on elephant limb bones some 1.5 million years ago. "As humans moved out of Africa and across the world, they took this type of technology with them," he said. Researchers studied the bones and archeological evidence for years. But it wasn't until recently that they were able to accurately estimate the date of the site. James Paces, a research geologist with the U.S. Geological Survey and co-author of the new study, used uranium-thorium dating from multiple bone specimens to determine their approximate age. He estimated the bones were about 130,000 years old, plus or minus 9,400 years, based on the distribution of naturally occurring uranium and its decay products. He said other methods, such as radiocarbon dating and luminescence dating — which measures the amount of light emitted from energy stored in rocks — had failed because of the bones' condition. "We now have a robust, defensible age for early humans being present in North America more than 100,000 years previous than what people had imagined," Paces told reporters. WATCH: This gene-editing technology has the potential to bring back the woolly mammoth</s>Researchers in Southern California have unearthed archaeological evidence that suggests humans lived in North America 130,000 years ago – predating previous estimates by over 100,000 years and throwing grave doubts upon what we thought we knew about the history of the continent.

The San Diego Natural History Museum announced the findings to the public on Wednesday.

NPR reports: In 1992, archaeologists working a highway construction site in San Diego County found the partial skeleton of a mastodon, an elephant-like animal now extinct. Mastodon skeletons aren’t so unusual, but there was other strange stuff with it.

“The remains were in association with a number of sharply broken rocks and broken bones,” says Tom Deméré, a paleontologist at the San Diego Natural History Museum. He says the rocks showed clear marks of having been used as hammers and an anvil. And some of the mastodon bones as well as a tooth showed fractures characteristic of being whacked, apparently with those stones.

It looked like the work of humans. Yet there were no cut marks on the bones showing that the animal was butchered for meat. Deméré thinks these people were after something else. “The suggestion is that this site is strictly for breaking bone,” Deméré says, “to produce blank material, raw material to make bone tools or to extract marrow.” Marrow is a rich source of fatty calories.

The scientists knew they’d uncovered something rare. But they didn’t realize just how rare for years, until they got a reliable date on how old the bones were by using a uranium-thorium dating technology that didn’t exist in the 1990s.

The bones were 130,000 years old. That’s a jaw-dropping date, as other evidence shows that the earliest humans got to the Americas about 15,000 to 20,000 years ago.

“That is an order of magnitude difference. Wow,” says John Shea, an archaeologist at New York’s Stony Brook University who specializes in studying ancient toolmaking. “If it’s correct, then there’s an extraordinarily ancient dispersal to the New World that has a very different archaeological signature from anything left behind by recent humans.”

Shea says it’s different because Stone Age toolmakers usually leave behind stone flakes — sharp pieces broken or “knapped” from certain kinds of rock that serve as cutting implements. There were none at the California site. Another odd thing: no signs that the mastodon was butchered for the meat.

“This is weird,” Shea says. “It’s an outlier in terms of what archaeological sites from that time range look like everywhere else on the planet.” He suggests these bones might have been broken up by natural causes — by a mudflow, perhaps, or by the trampling of animals sometime after the mastodon died.

Another skeptic is John McNabb, an archaeologist at the University of Southampton in England. His question: How did those people get to California?

Twenty thousand years ago, archaeologists agree, people did cross over to Alaska from Siberia, perhaps more than once. Sea levels were lower then and there was a land bridge connecting the continents. In an interview with the journal Nature, which published the California research, McNabb says that land bridge wasn’t there 130,000 years ago. “The sea lane in between the two continents [was] wider [then],” he says, “so that’s one problem with this: How do we get humans across?”

McNabb says what’s needed to really prove that this is truly an archaeological site are bones from the people who got there.

The California team counters that it has spent over 20 years examining the evidence. “I know people will be skeptical with this because it is so surprising,” says team member and archaeologist Steve Holen, “and I was skeptical when I first looked at the material myself. But it’s definitely an archaeological site.”

Holen, with the Center for American Paleolithic Research, says these early people could have come across in boats. As for the broken bones, he says the type of fracture isn’t accidental. And the way the hammerstones and bones were distributed in the ground doesn’t look natural.

One question the team can’t answer is who these people were. A genetic technique that uses mutations in a population’s genome as a sort of “clock” says the first common ancestor of Native Americans lived about 20,000 years ago. So if there were indeed earlier settlers, it could be they made an arduous migration from Siberia, only to die out without leaving any descendants.
A speculative study hypothesizes that a species of Homo may have lived in California 130,000 years ago.