links for 2007-02-24

New Dates for Clovis

From the, “Now That It Has Been Published, We Can Talk About This” Department

This is how it is done, folks. Peer-reviewed prior to hitting the press.

A new bone collagen radiocarbon (14C) dating technique, resample some things, sample others for the first time (!) and away you go. [Side note: only 22 sites with Clovis or Clovis-like material had been directly dated prior to this study.]

The summary and the article by Waters and Stafford, both from the current issue of Science.

Redefining the Age of Clovis: Implications for the Peopling of the Americas [Waters and Stafford, Science 23 February 2007]
[abstract] The Clovis complex is considered to be the oldest unequivocal evidence of humans in the Americas, dating between 11,500 and 10,900 radiocarbon years before the present (14C yr B.P.). Adjusted14C dates and a reevaluation of the existing Clovis date record revise the Clovis time range to 11,050 to 10,800 14C yr B.P. In as few as 200 calendar years, Clovis technology originated and spread throughout North America. The revised age range for Clovis overlaps non-Clovis sites in North and South America. This and other evidence imply that humans already lived in the Americas before Clovis. [emphasis added –ed.]

For nearly 50 years, it has been generally thought that small bands of humans carrying a generalized Upper Paleolithic tool kit entered the Americas around 11,500 radiocarbon years before the present (14C yr B.P.) and that these first immigrants traveled southward through the ice-free corridor separating the Laurentide and Cordilleran Ice Sheets. These people developed the distinctive lithic, bone, and ivory tools of Clovis and then quickly populated the contiguous United States. Clovis humans and their descendants then rapidly populated Central America and reached southernmost South America by 10,500 14C yr B.P.

Identifying when the Clovis complex first appeared and knowing the complex’s duration is critical to explaining the origin of Clovis, evaluating the Clovis-first model of colonization of the Americas, determining the role of humans in the extinction of late Pleistocene megafauna, and assessing whether people inhabited the Americas before Clovis. We determined a more accurate time span for Clovis by analyzing the revised existing Clovis 14C date record and reporting high-precision accelerator mass spectrometry (AMS) 14C ages from previously dated Clovis sites. Our AMS 14C dates are on culturally specific organic matter—bone, ivory, and seeds—that accelerator mass spectrometers can date accurately to precisions of ±30 years at 11,000 14C yr B.P. (…)

Here is a popular-press article in the Houston Chronicle, “A&M find may shatter land-bridge migrant theory: A&M research raises migration doubt.” (I’m linking to the Chron because Eric Berger actually spoke with the researchers.)