aCenter of Excellence in Remote Sensing Education and Research, Elizabeth City State University, Elizabeth City, NC 27921
bSouth Carolina Institute of Archaeology and Anthropology, University of South Carolina, Columbia, SC 29208;cDepartment of Geography, University of Delaware, Newark, DE 19716;dAnalytical Instrumentation Facility, North Carolina State University, Raleigh, NC 27695;eDepartment of Psychology, University of Oregon, Eugene, OR 97403;fInstitute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH 03824; andgSeidel Research, Camden, NC 27921
Edited by* Steven M. Stanley, University of Hawaii, Honolulu, HI, and approved August 7, 2012 (received for review May 22, 2012)
Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA106:16016–16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 calendar years ago, Firestone et al. reported discovery of markers, including nanodiamonds, aciniform soot, high-temperature melt-glass, and magnetic microspherules attributed to cosmic impacts/airbursts. The microspherules were explained as either cosmic material ablation or terrestrial ejecta from a hypothesized North American impact that initiated the abrupt Younger Dryas cooling, contributed to megafaunal extinctions, and triggered human cultural shifts and population declines. A number of independent groups have confirmed the presence of YDB spherules, but two have not. One of them [Surovell TA, et al. (2009) Proc Natl Acad Sci USA 104:18155–18158] collected and analyzed samples from seven YDB sites, purportedly using the same protocol as Firestone et al., but did not find a single spherule in YDB sediments at two previously reported sites. To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell et al. We found abundant YDB microspherules at all three widely separated sites consistent with the results of Firestone et al. and conclude that the analytical protocol employed by Surovell et al. deviated significantly from that of Firestone et al. Morphological and geochemical analyses of YDB spherules suggest they are not cosmic, volcanic, authigenic, or anthropogenic in origin. Instead, they appear to have formed from abrupt melting and quenching of terrestrial materials.
Did a massive comet explode over Canada 12,900 years ago, wiping out both beast and man in North America and propelling the earth back into an ice age?
That’s a question that has been hotly debated by scientists since 2007, with the University of South Carolina’s Topper archaeological site right in the middle of the comet impact controversy. However, a new study published today (Sept.17) in the Proceedings of the National Academy of Sciences (PNAS) provides further evidence that it may not be such a far-fetched notion.
To eliminate potential analytical bias, we participated in a blind test of the sediment samples taken from the two common sites, BWD and TPR. Blind testing was not applicable for the single sample collected from PPC. The eight unprocessed sediment samples, four from each site, were repackaged and distributed by a non-participating third party for blind processing by a member of our group (MAL). The packages were randomly numbered and labeled with the indicated source site, but not with depth or relationship to the YDB layer. At the conclusion of the blind test, we adopted the same chronostratigraphy used by the principal investigators for all of our sites, as well as by Firestone et al. and Surovell et al. YDB depths may vary between studies due to differences in the sampled locations.