A sharp controversy concerning a rock-dating method

The geology community is evidently in the midst of an apparent scandal concerning the rock-dating data produced by a prominent researcher. The elements of the story are as follows:

    1) Data from Ronald Dorn (Arizona State University Tempe, US) concerning hundreds of petroglyphs, stone tools, and rock surfaces around the world are in question.

    2) These data were produced by a method of dating the organic material in rock varnish samples (see below). It is being reported that rock varnish samples processed by Dorn contain microscopic granules of coal and charcoal, which it is said render the dating results meaningless, with implications for such debates as the peopling of the Americas.

    3) The carbon granules evidently do not appear in samples processed by other researchers, and it said the US National Science Foundation and Arizona State University are reviewing the possibility of misconduct.

    4) Dorn is reported to acknowledge that his technique is flawed and produces "ambiguous" results. But he says the suggestion of tampering is "utterly false" and that the carbon granules are naturally occurring.

    5) The technique in question involves accelerator mass spectrometry radiocarbon analysis, one of several rock-surface dating methods pioneered since the 1980s by Dorn.

The method assumes that microscopic quantities of carbon-rich organic material become trapped in and beneath a thin layer of natural varnish on the rock surface. Although some specialists have doubted the trapped material can be accurately dated, Dorn has argued since 1986 that the material holds measurable quantities of radioactive carbon- 14, which decays at a known rate. To date a rock, Dorn scrapes the varnish and material beneath the varnish, extracts the organic material with acid, then sends samples to various accelerator mass spectrometry facilities. This controversy is apparently serious enough so that most geologists are now considering all of Dorn's data suspect, and rock-varnish dating in general of significantly reduced utility. A technical commentary by Beck et al (7 authors at 4 installations, US CH) has been published to alert the geology community to the problem.

QY: David Malakoff science_editors@aaas.org
QY: W. Beck, University of Arizona 520-621-2211.
(Science 26 Jun 98 280:2132) (Science-Week 17 Jul 98)

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