Rock Dates Thrown Into Doubt, Researcher Under Fire

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Science  26 Jun 1998:
Vol. 280, Issue 5372, pp. 2041-2042
DOI: 10.1126/science.280.5372.2041

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The age of some striking Arizona petroglyphs is being called into question in a Technical Comment in this issue (p. 2132) challenging the validity of the technique used. The method uses accelerator mass spectrometry radiocarbon analysis to date microscopic quantities of carbon-rich organic material that are believed to become trapped beneath a thin layer of natural varnish on rocks. The researcher who pioneered the method acknowledges that his technique is flawed and produces "ambiguous" results but counters that faulty lab technique explains why other researchers have been unable to replicate his results. The controversy has sparked inquiries by the National Science Foundation and the university where the research was performed and is likely to cast a cloud over rock-varnish science as a whole.