美国国家公共电台 NPR New Evidence Suggests Humans Arrived In The Americas Far Earlier Than Thought

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Artifacts found in Southern California have puzzled scientists for years. Some now say they are proof that humans lived in the area 130,000 years ago, well before anyone thought. That would make them the oldest evidence of humans in the Americas ever. As NPR's Christopher Joyce reports, scientists are wondering whether or not to believe it.

CHRISTOPHER JOYCE, BYLINE: In 1992, archaeologists working on a highway construction site found a partial skeleton of a mastodon, an elephant-like animal now extinct. Mastodon skeletons aren't that unusual, but there was other strange stuff with it.

TOM DEMERE: The remains were in association with a number of sharply broken rocks and broken bones.

JOYCE: Tom Demere is a paleontologist at the San Diego Natural History Museum. He says the rocks showed clear marks of having been used as a hammer and anvil. And some of the mastodon bones as well as a tooth showed fractures characteristic of being whacked with those stones. It looked like the work of humans, yet there were no cut marks on the bones showing that it was butchered for meat. Demere thinks these people were after something else.

DEMERE: The suggestion is that this site is strictly for breaking bones to produce blank material, raw material to make bone tools or to extract marrow.

JOYCE: The scientists knew they'd uncovered something rare, but they didn't realize just how rare for years until they got a reliable date on how old the bones were - 130,000 years old. Now, that's a jaw-dropping date because the best evidence up to now shows that the earliest humans got here about 15,000 to 20,000 years ago.

JOHN SHEA: That's an order of magnitude difference. That is - wow.

JOYCE: John Shea is an archaeologist at Stony Brook University.

SHEA: If it's correct, then there is an extraordinary ancient dispersal to the New World that has a very different archaeological signature.

JOYCE: Shea says it's different because Stone Age humans usually leave behind sharp flakes - bits of stone used for cutting. There were none at the California site. Another odd thing - no signs that the mastodon was butchered.

SHEA: This is weird. It's an outlier in terms of what archaeological sites from that time range look like everywhere else on the planet.

JOYCE: Shea suggests that these bones might have been broken naturally by a mudflow or trampled by animals. Also skeptical is John McNabb, an archaeologist at the University of Southampton in England. He wondered how these people got here.

Twenty thousand years ago, people did cross over to Alaska from Siberia. Sea levels were lower, and there was a land bridge. In an interview with the Journal Nature, which published the research, McNabb's says that land bridge was not there 130,000 years ago.

JOHN MCNABB: The sea lane in between the two continents is wider. So that's one problem with this. How do we get humans across?

JOYCE: The California team says they're sure of their conclusion. Archaeologist Steve Holen is with the Center for American Paleolithic Research.

STEVE HOLEN: I know people will be skeptical of this because it is so surprising, and I was skeptical when I first looked at the material myself. But it's definitely an archaeological site.

JOYCE: Holen says these early people could have come across in boats. As for the broken bones, he says the types of fractures are not accidental. One question the team cannot answer is, who were these people? Genetic studies indicate that the first ancestors of Native Americans date back only to 20,000 years. If there were indeed earlier settlers, it could be they died out without leaving any descendants. Christopher Joyce, NPR News.