Mammoth bones, ‘ghost’ footprints: Did humans arrive in North America much earlier than we thought?

Recent discoveries of mammoth bones and “ghost” footprints left behind by ancient peoples are adding fuel to a scientific debate over whether the first humans to reach North America may have come much earlier than previously thought.

Scientists generally agree that the first people to live in what is now Canada and the United States arrived around 10,000 to 15,000 years ago and may have walked from Asia over a “land bridge” that covered the Bering Strait. But these new discoveries have been dated much earlier than 10,000 years ago, calling into question this timeline of human migration to North America.

In a study published on July 7, researchers detailed the discovery of two mammoth fossils, a mother and her calf, found in New Mexico. The bones have been radiocarbon dated to around 37,000 years ago and patterns of fractures on the bones show evidence that humans may have butchered them for meat.

The fossils were found on rocks high above a tributary to the Rio Grande in what is now called the Hartley site. Bone markings appear to show where humans chopped meat and placed puncture marks to drain grease from ribs and vertebral bones. A high number of bone flakes, which is characteristic of butchering, were also found.

A chemical analysis of sediment around the bones showed fire particles that came from a sustained and controlled burn, unlikely to have been caused by nature. The material also contained bone fragments and the remains of fish and small animals, despite the site being 60 metres away from the closest river.

An article by the University of Texas (UT) calls the find “some of the most conclusive evidence for humans settling in North America much earlier than conventionally thought.”

“What we’ve got is amazing,” said lead author Timothy Rowe, a paleontologist and a professor at the UT Jackson School of Geosciences. “It’s not a charismatic site with a beautiful skeleton laid out on its side. It’s all busted up. But that’s what the story is.”

But not everyone in the scientific community is so thrilled with Rowe’s conclusions.

Andre Costopoulos, a professor at the University of Alberta in Edmonton, posted his own analysis of the research in an online blog post. He’s not convinced that this mammoth graveyard was due to human hands, positing that a landslide could have caused the same signatures.

“The extensive breakage is consistently described as systematic, but the authors also emphasize that the material was buried in a single event, shortly after death, which suggests a catastrophic event. As we know from the eolith debate, humans are not the only and necessary source of systemic patterning in nature,” Costopoulos wrote.

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But even Costopoulos admits that the findings are exciting, even if he’s not convinced they represent conclusive evidence of human presence.

“The strongest and most intriguing evidence presented is not from the mammoth bones at all, but from possibly burned vertebrate microfauna, including fish teeth and scales found in the soil. I will say that without some sort of animal agent, human or other, the fish bones cemented into calcified aggregates are harder to explain than the broken mammoth bones,” he wrote.

Meanwhile, on July 26, the Cornell Chronicle announced that a Cornell researcher has found 88 preserved “ghost” footprints in the salt flats of the U.S. Air Force’s Utah Testing and Training Range. The markings, dated to around 12,000 years ago, are called “ghost” footprints because they become visible when the ground is wet enough but disappear when the earth dries again.

This discovery mirrors an earlier ghost footprint finding in New Mexico’s White Sands National Park that was dated to 21,000 years ago, though its dating is disputed by scientists.

“Based on excavations of several prints, we’ve found evidence of adults with children from about five to 12 years of age that were leaving bare footprints,” Daron Duke, of Far Western Anthropological Research Group, said in an Air Force press release. “People appear to have been walking in shallow water, the sand rapidly infilling their print behind them — much as you might experience on a beach — but under the sand was a layer of mud that kept the print intact after infilling.”

What is now a salt flat was likely a wetland 10,000 years ago, providing the perfect conditions for these footprints to be made by wading ancient humans.

It will likely take more evidence, though, to convince most scientists to push back the timeline of human arrival in North America, something that Spencer Lucas, the curator of paleontology at the New Mexico Museum of Natural History and Science, bemoans.

“The research looks very thorough,” said Lucas in an interview with NBC News. “At what point will the archaeological community wake up and smell the coffee? There’s so much evidence,” he said.

“I’m not saying this is the final piece of evidence … but you’ve got the White Sands footprints, and the (Mexico) site — there’s all sorts of evidence accumulating 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.”