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13-Sep-2019 07:41

For decades, archaeologists have searched North and South America for the oldest evidence of occupation.

Last year, Canadian researchers reported that bones of caribou and other mammals found in the Yukon with cut marks, which they argue were man-made, date back 24,000 years. Waters, an archaeologist at Texas A&M University, and his colleagues reported that a stone knife and mastodon bones with cut marks found in a Florida sinkhole are about 14,500 years old.

That test revealed, to their surprise, that the bones were 130,000 years old.

Yet the fractures suggested the bones were still fresh when they were broken with the rocks.

There’s a great deal of evidence for that kind of activity at older sites in other parts of the world, he noted. Mandel, a geoarchaeologist at the University of Kansas who was not involved in the study, found it hard to see how the rocks and bones could come together without the help of people. But other archaeologists said the bone fractures and rock scratches were unconvincing.“They present evidence that the broken stones and bones could have been broken by humans,” said Vance T.

Another mysterious lineage of humans, the Denisovans, split off from Neanderthals an estimated 400,000 years ago. To Beth Shapiro, a paleogeneticist at the University of California, Santa Cruz, the idea that Denisovans or Neanderthals could have made the trek from Asia to North America is plausible.

A team of paleontologists from the museum spent the next five months excavating the layer of sediment in which they were found.

The team discovered more scattered bone fragments, all of which seemed to have come from a single mastodon. The thick bones were broken and smashed, and near the animal were five large rounded stones. Deméré and his colleagues invited other experts to help determine how the bones were broken apart.

“But they don’t demonstrate that they could only be broken by humans.”Gary Haynes, an archaeologist at the University of Nevada, Reno, said the researchers should have ruled out more alternatives.

Some of the bone fractures could have been caused by pressure from overlying sediment, he suggested. Deméré and his colleagues struggled to figure out how long ago the mastodon died. Paces, a research geologist at the United States Geological Survey, who determined how much uranium in the bones had broken down into another element, thorium.

Another mysterious lineage of humans, the Denisovans, split off from Neanderthals an estimated 400,000 years ago. To Beth Shapiro, a paleogeneticist at the University of California, Santa Cruz, the idea that Denisovans or Neanderthals could have made the trek from Asia to North America is plausible.

A team of paleontologists from the museum spent the next five months excavating the layer of sediment in which they were found.

The team discovered more scattered bone fragments, all of which seemed to have come from a single mastodon. The thick bones were broken and smashed, and near the animal were five large rounded stones. Deméré and his colleagues invited other experts to help determine how the bones were broken apart.

“But they don’t demonstrate that they could only be broken by humans.”Gary Haynes, an archaeologist at the University of Nevada, Reno, said the researchers should have ruled out more alternatives.

Some of the bone fractures could have been caused by pressure from overlying sediment, he suggested. Deméré and his colleagues struggled to figure out how long ago the mastodon died. Paces, a research geologist at the United States Geological Survey, who determined how much uranium in the bones had broken down into another element, thorium.

But the mastodon bones in San Diego are vastly older than any others said to show evidence of human manipulation — so old that they may not represent the work of our own species.