| ROCK ART DATINGS WITHDRAWN |
 ROCK ART DATINGS
WITHDRAWNOne of the world’s foremost rock art dating scientists, Professor Ronald I. Dorn of the Geography Department of Arizona State University, has just retracted the results of all of his own research work, negating effectively all he has produced during his professional career of about fifteen years. He published a very short paper entitled ‘A change of perception’ in a minor American newsletter, La Pintura. In it he states that he ‘made two critical mistakes on the radiocarbon dating of organic matter associated with rock varnish’, the method he says he was the developer and proponent of. First, he says, he treated the organic matter associated with varnish as a homogenous bulk sample. Second, he assumed that varnishes have a closed carbon system, similar to what he thought he had observed on basalt flows. He concedes that it had been naive of him ‘to expect that no organic weathering occurred before a petroglyph panel was exposed’ to weathering. These admissions indicate indeed extraordinary naivety. Even from Dorn’s own previous work, especially from the excellent microscopic sections of varnishes he published, it is clear that their nanostratigraphies can be very complex. This was shown by others before him, for instance by R. G. Bednarik. Nanostratigraphical work he underook over twenty years ago also showed conclusively that ferromanganeous accretionary mineral deposits were open carbon systems. In 1979 he published (The Artefact 4: Fig 3) not only evidence that organic matter occurs even in the unaltered rock core, but also that its concentration increases more than 18-fold towards the surface-nearest stratum. This pattern clearly indicates free access to atmospheric carbon sources. Unfortunately for Dorn and the discipline that relied on his findings for one and a half decades, he was either not aware of this previous research, or has ignored its implications for his work. The result has been a monumental blunder. Hundreds of archaeologists, geologists and geographers, both in America and abroad, have relied heavily on his ‘dating’ results. Many alternative projects have no doubt been neglected, papers submitted for publication rejected, and so on. Numerous archaeological hypotheses are in some direct or indirect way contaminated by concepts derived from Dorn’s results, because of the long duration of this affair, and researchers who have opposed him in the past have been ostracised for it. Opposition to his methods began in Australia, when they were subjected to vigorous debate in Rock Art Research in 1988. This led to attempts by Dr Alan Watchman in the early 1990s to duplicate some of Dorn’s research. Watchman’s totally different results in turn prompted an investigation by four radiocarbon scientists at the NSF AMS Facility, Department of Physics, University of Arizona. They examined samples submitted by Professor Dorn microscopically and found them to consist of two types of black, carbon-rich substances, strongly resembling ground charcoal and finely ground bitumenous coal. Warren Beck, Douglas Donahue, G. Burr and A. J. T. Jull then analysed duplicate samples taken from the same petroglyphs Dorn claims to have sampled, and detected no such substances in the rock varnish. They have since analysed ‘splits’ from older samples submitted by Dorn, with similar results. It is interesting that Dorn’s momentous retraction of all his results coincided with the report of the investigation into his samples, an investigation he is reported to have co-operated with. It also coincided with his submission of another article to Antiquity, in which he also casts grave doubts on all his dating results, and even rejects them in favour of the results of an untested and highly experimental method, cosmogenic radiation ‘dating’. It will be interesting to see what the academic community of the United States is going to do about the considerable academic honours it has heaped on Professor Dorn, including the medal of the most outstanding young scientist of the year (he became a professor at 27). Unfortunately, the matter does not end here. Rock art dating, with its credibility already stretched by unrealistic expectations of archaeologists and by over-interpretation of analytical results, has suffered other setbacks recently, including the hysterical reaction of European Pleistocene archaeologists to the age estimates for the Côa petroglyphs in Portugal, and the unfortunate handling of the claims concerning the Jinmium petroglyph site in the Northern Territory. Robert G. Bednarik |
