Oops--Having To Rewrite American Prehistory

One of the anomalies in American prehistory were that settlements at the Monte Verde archaeological site in Chile dated back to 14,500 years ago--older than the earliest human settlements found in North America. It sparked huge debates on how South American could have been settled first, from early seafarers traveling across the Pacific Ocean to human settlement leapfrogging down the Pacific Coast before spreading inland. But Popular Mechanics is now reporting that the 14,500 B.C. date may be wrong:

    Monte Verde is certainly ancient, but as it turns out, evidence of human occupation at the site is not quite as ancient as it was once believed to be. Anthropologist Todd Surovell (from the University of Wyoming) and his team of researchers have found that the site was only occupied between 4,200 and 8,200 years ago. 

[snip]

    According to the researchers, several critical observations had been missed. For one, Monte Verde II is actually above an older layer known as Lepué Tephra, which is comprised of rock fragments that were ejected by an erupting volcano. And that lower (and, therefore, presumably older) layer is only 11,000 years old—nowhere close to the original 14,500-year-old estimate for Monte Verde occupation. For another, the original investigation of the site never accounted for the erosion that further separates older and younger strata in the region.

    There is also a significant presence of Pleistocene wood and organic matter near Monte Verde II, which is about the same age as wood at the site itself. Because of geological disruptions in the region during Early Holocene, organic matter dating back to the Pleistocene was exposed, redeposited, and buried in river sediments that Surovell dated to the Middle Holocene. This natural phenomenon convinced previous archaeological teams that the settlement at Monte Verde II was far older than it actually was, even leading some to reject the theory of human migration over the Beringia land bridge. The age of the sediments can only mean that whatever remained of the Monte Verde settlement was from the Middle Holocene, rather than the Pleistocene. While this does not necessarily rule out human presence in the Americas before the Clovis culture, there has not yet been sufficient evidence to confirm that anyone predated them.