Mammoth bones and “ghost” footprints from ancient humans are the latest evidence in a scientific debate over when the first humans reached the Americas.
The fossilized bones in particular could suggest that people lived in North America tens of thousands of years before the generally accepted date of the arrival of the first Native Americans around 10,000 BC.
Scientists say radiocarbon dates of chemicals in mammoth bones, from a mother and her calf, indicate the animals lived about 37,000 years ago in what is now New Mexico. Fracture patterns on the bones show that they were butchered by humans, who must therefore have lived there at the same time, the researchers added. But the findings are disputed by some other researchers, who say the fractures may have been caused naturally.
The latest “ghost” footprints, meanwhile, were found a few weeks ago on an Air Force missile range in a Utah desert. Scientists believe they are around 12,000 years old, but this is only the second time such footprints have been found, and they support the discovery of ghost footprints in New Mexico last year, thought to be at least 21,000 years old – although this find, too, is disputed.
The mammoth bones at what is called the Hartley site in northern New Mexico, on rocks high above a tributary of the Rio Grande, are hailed as the most conclusive evidence yet that humans arrived in the Americas up to 50,000 years ago and crossed a “land “bridge” between what is now Siberia and Alaska.
The researchers say they are confident of the dating and interpretation that the fractures on them were caused by repeated impacts with sharp objects during deliberate butchering. They also say there is evidence that fire was used selectively to cook many of the bones.
“I think that’s a rock-solid radiocarbon date,” said paleontologist Timothy Rowe, a professor at the Jackson School of Geosciences at the University of Texas at Austin. “Skeptics will put everything under the microscope, but I think we checked every box.”
Rowe is lead author of a study of mammoth bones published last month in the journal Frontiers in Ecology and Evolution.
He said the fractures and tiny bone flakes caused by the butchering process are also distinctive and seen at butcher sites of the same age in Europe and Asia: “If this place was in northern Siberia, no one would blink.”
The idea that the mammoths were butchered by early humans is supported by other recent finds, including the human footprints at White Sands National Park in New Mexico and what are said to be stone tools made 33,000 years ago in a cave in northern Mexico.
But the idea, and the evidence, is disputed by other researchers. The dating of the White Sands footprints has been questioned, and some researchers believe the artifacts from Mexico are not tools at all, but naturally pointed stones.
And they dispute that the fractures on the mammoth bones can only have been made by humans; instead, they may have been caused by a landslide or other natural event.
“The patterns of fractures on those mammoth bones at that site could definitely be caused by humans,” said anthropologist Andre Costopoulos, a professor at the University of Alberta in Edmonton, who has posted a detailed online examination of the latest research. “But they are not necessarily diagnostic of a human presence.”
“We don’t have clear evidence yet, because there are other possible explanations that need to be ruled out first, and they haven’t been,” he said.
The absence of characteristic stone tools at the Hartley site is also a problem. The researchers say that the people who butchered the mammoths may not have used sophisticated stone tools, but only primitive tools indistinguishable from natural bones or stones.
But other researchers say there is no evidence for this, and that even primitive humans at this time can be expected to have better tools.
Archaeologist Ben Potter, formerly of the University of Alaska Fairbanks and now of Liaocheng University in China, said there is evidence from Africa, Europe and the Far East that Homo sapiens used complex stone tools starting around 47,000 years ago, and that their absence on The Hartley site is significant.
He said in an email that he is not convinced by the latest research on the mammoth bones and the idea that it shows people came to America that long ago. “Anything is possible. But we just have to have evidence to support the claim,” he said. “I don’t think they have sufficient evidence yet, and certainly not on this site.”
Some other researchers, however, are more convinced, suggesting that others may be reluctant to face the possibility that some people arrived in the Americas as long ago as 50,000 years ago.
“The research looks very thorough,” said Spencer Lucas, curator of paleontology at the New Mexico Museum of Natural History and Science. “At what point will the archaeological community wake up and smell the coffee? There is so much evidence,” he said.
“I’m not saying this is the final piece of evidence…but you have the White Sands footprints, and [Mexico] website — all kinds of evidence is piling up that points to human occupation of the New World before 20,000 years ago, and I don’t understand why that idea is still worth arguing about.”