No evidence of nanodiamonds in Younger–Dryas sediments to support an impact event
Tyrone L. Daulton a,1, Nicholas Pinter b, and Andrew C. Scott c
-Author Affiliations
aDepartment of Physics and Center for Materials Innovation, Washington University in St. Louis, St. Louis, MO 63130;
bDepartment of Geology, Southern Illinois University, Carbondale, IL 62901; and
cDepartment of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 OEX, United Kingdom
Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved July 27, 2010 (received for review March 24, 2010)
Abstract
The causes of the late Pleistocene megafaunal extinctions in North America, disappearance of Clovis paleoindian lithic technology, and abrupt Younger–Dryas (YD) climate reversal of the last deglacial warming in the Northern Hemisphere remain an enigma. A controversial hypothesis proposes that one or more cometary airbursts/impacts barraged North America ≈12,900 cal yr B.P. and caused these events. Most evidence supporting this hypothesis has been discredited except for reports of nanodiamonds (including the rare hexagonal polytype) in Bølling–Ållerod-YD-boundary sediments. The hexagonal polytype of diamond, lonsdaleite, is of particular interest because it is often associated with shock pressures related to impacts where it has been found to occur naturally. Unfortunately, previous reports of YD-boundary nanodiamonds have left many unanswered questions regarding the nature and occurrence of the nanodiamonds. Therefore, we examined carbon-rich materials isolated from sediments dated 15,818 cal yr B.P. to present (including the Bølling–Ållerod-YD boundary). No nanodiamonds were found in our study. Instead, graphene- and graphene/graphane-oxide aggregates are ubiquitous in all specimens examined. We demonstrate that previous studies misidentified graphene/graphane-oxide aggregates as hexagonal diamond and likely misidentified graphene as cubic diamond. Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the YD impact hypothesis.
archaeology paleoclimate Quaternary extinctions carbon spherules fungal sclerotia
Footnotes
1To whom correspondence should be addressed. E-mail:tdaulton@physics.wustl.edu.
Author contributions: T.L.D., N.P., and A.C.S. designed research, performed research, analyzed data, and wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
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