Exactly how long have humans been in the Americas? A wealth of evidence suggests they arrived as early as 20,000 years ago, while the earliest record of modern humans in the world dates back 200,000 years to Africa (and they probably didn't leave until around 50,000 to 80,000 years ago). But researchers at the San Diego Natural History Museum say they've unearthed evidence that humans, or at least "an unidentified species of Homo," were here 130,000 years ago—a "bold and fiercely disputed claim," per the New York Times, based on mastodon bones and rock scratches found in Southern California in 1992. The claim, published in the journal Nature, is that the markings suggest the use of tools to extract marrow or process bone material to create more tools.
Critics aren't holding back. "Extraordinary claims require unequivocal evidence," one skeptic says, while an archaeologist adds: "I was astonished, not because it is so good but because it is so bad." Others think such an early arrival is conceivable. For instance, the Denisovans broke from Neanderthals around 400,000 years ago and lived in Siberia, while bison came to North America by way of the Bering Land Bridge—which has disappeared and reappeared—135,000 years ago. What everyone agrees on is that the mastodon bones, which NPR reports were measured using sophisticated uranium-thorium dating tech, are 130,000 years old. If a human-like species cut them, it's "an order of magnitude difference," one researcher says. "Wow." (Our family tree is still very much a puzzle.)