“How did they get there?” says Deméré. “They weren’t being transported by flowing water at Skiptrace Pro the same time as the silt.” Instead, he suggests that they were carried to the site and used to infiltrate the mastodon bones—presumably to get at the marrow within. Sure enough, the rocks showed signs of impact, and the team even managed to fit several detached flakes back onto the “parent” stones. Could these patterns have been caused by anything else? Could the bones have been trampled by heavy feet, chewed or crunched by scavengers, or displaced and eroded by water? “I cannot envision another scenario than human involvement that introduces heavy mastodon bones, lighter mastodon bones, and heavy cobbles into an otherwise well-sorted, fine-grained matrix,” says Pitblado. And Deméré adds that his team took care to rule out alternative explanations. “It’s the totality of the site—all these different lines of evidence that can’t be Skip Tracing Tool explained by processes other than human activity,” he says. But “nature is mischievous and can break bones and modify stones in a myriad of ways,” says Meltzer, who thinks that the evidence is “inherently ambiguous.” Ariane Burke from the University of Montreal adds that the fractures are consistent with the bones having been struck by a heavy object while still fresh—but it’s not clear if humans did the striking. The problem is that in focusing on the fractures, the team haven’t published information on the rest of the bones, which might reveal signs of weathering or other natural abrasions. “It is one thing to show that broken bones and modified rocks could have been produced by people, which they’ve done,” says Grayson.
For the original version including any supplementary images or video, visit https://www.theatlantic.com/science/archive/2017/04/new-study-puts-humans-in-america-100000-years-earlier-than-expected/524301/