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The archaeology community is buzzing about two new scientific studies that challenge what we thought we knew about the first humans in the Americas. These studies were both published in the journal Nature on July 22nd, and they provide surprising evidence that people were on this landmass some 10 to 15 thousand years earlier than archaeologists previously thought.

Which, as they say, is “big, if true”. For a long time, the oldest evidence we had of humans in the Americas were artifacts dating to around 13,000 years ago. These are attributed to a group of humans called the Clovis people who traveled from modern-day Russia to the northwest tip of North America via a bridge of land that used to exist when sea levels were lower.

But in recent decades, evidence has been popping up that suggests humans were here even earlier than that. But exactly how much earlier has been the big question— and a source of heated debate. The authors of the two new studies have leapt headfirst into this controversy by claiming that people have lived in the Americas for at least 30 thousand years.

Though they would have taken the same bridge, that could mean they took a different route to South America or across the continent —so, maybe, we've been looking in all the wrong spots for evidence of early peoples. And it could have major implications for how we interpret the effects of our species—like, how these early people impacted local wildlife, depending on whether they arrived before or after key extinctions. The researchers arrived at that 30 thousand-ish figure using two different kinds of evidence.

The first is your classic archaeological study: they report stone tools from Chiquihuite Cave in the mountains of northern Mexico which date back that far. A team of dozens of international scientists carefully excavated and examined three meters of layered sediment containing over 1900 angular pieces of limestone. And they believe that, based on the shapes and wear on these stones, they're bona fide human-made tools, even though they're different from the tools of every other ancient culture that we know of.

And, using a combination of dating techniques, the researchers found that some of the sediment layers containing these objects are 30 thousand years old! That would mean that not only had humans made it to North America by that time, they had already spread all the way down into Mexico! This clashes with most accepted archaeological evidence, but is totally in line with the results of the second new study, which comes from two of the first study's authors.

In this one, the pair compiled information from 42 archaeological sites to create a statistical model that makes predictions about how people spread across the continent. And what's interesting is that this model suggests a similar narrative: that humans were likely in North America 26 thousand years ago, and possibly earlier. But extraordinary results tend to receive intense scrutiny from other scientists, and that's definitely happening here.

One major sticking point is the nature of the quote “stone tools”. Some experts aren't convinced that that's what they are. It can be difficult to tell a rock that's been broken intentionally by humans from a rock that was damaged by more mundane things— like the collapse of a cave ceiling.

Though, in this case, the stones had to have come from outside the cave, as the kind of stone didn't match the cave itself. But still, they could have washed in during a flood, or something like that. So, critics say the authors haven't provided enough evidence against that kind of non-human explanation.

But the authors say the tools speak for themselves. Additionally, while the authors of the new study identify the cave as a human dwelling place, other experts don't think the evidence supports that conclusion. They haven't found human remains or even DNA, for instance.

The authors say that's because the cave wasn't a permanent home— it was probably more of a last-ditch shelter, perhaps used every few decades during really harsh winters. Given how difficult it can be to identify sites like this, and how important they are to our own history, disputes like these are not unusual. Similar sites in South America have alleged to have evidence of humans from over 20,000 years ago—and they, too, were questioned.

Some experts have pointed out that these sites tend to be highly disputed or even ignored by many archaeologists simply because they don't fit the more accepted story and evidence. But, to be fair, the evidence they provide isn't as clear cut. And their controversial nature might be a source of trouble for that second, statistical study.

You see, outside experts have pointed out that some of the archaeological sites used in the model are disputed in terms of their age or the identification of their artifacts. Indeed, the Chiquihuite Cave is one of the sites used. And if these places don't turn out to be sites where ancient humans were, then the model itself — and its intriguing results — might also be flawed.

If there's one thing everyone agrees on, though, it's that all of this is worth investigating further. If humans really were in the Americas 25-plus thousand years ago, then more investigation of these super-old sites should reveal more conclusive evidence. And there should be other, as of yet undiscovered sites that can give us a better idea of when, where, and how humans were making their way across this hemisphere.

While it might seem like our understanding of the past is kind of a mess, it's important to keep in mind that this is how science works. Pretty much everything we know about this planet and how we got to where we are today was once a wild idea that challenged the status quo. Of course, there have also been lots of wild ideas that didn't pan out.

So, without more data, we can't be sure whether the idea of 30 thousand year-old North American people is a game-changer or not. So, as is so often the case in archaeology, clearer answers are waiting to be dug up. Thank you for watching this episode of SciShow News!

And an extra thank you to today's President of Space, Harrison Mills. We checked, and the evidence is incontrovertible: you're awesome, Harrison! And so are our other patrons on Patreon.

We are so lucky to have such an engaged, science-loving community that supports SciShow. If you'd like to learn more about that community or how you can become. President of Space like Harrison, head on over to Patreon.com/SciShow. [♪ OUTRO].