Cave paintings in Spain need to be analyzed further before the works can be confirmed as the oldest known examples in the world, an archaeologist said, casting doubt over a paper published in the journal Science.
A team led by Alistair Pike of the University of Bristol in England said in the paper that paintings at El Castillo cave date back at least 40,800 years. That would make them about 4,000 years older than those at the Chauvet cave in France, meaning the Spanish works could be the only cave art ever found to have been painted by Neanderthals, according to Pike.
The findings at El Castillo need further confirmation, Jean Clottes, who led the research team that appraised the Chauvet works in 1998, said in a telephone interview. Pike’s team used a method based on the radioactive decay of uranium to analyze calcium carbonate crusts formed on top of the paintings. This contrasts with radiocarbon dating employed at Chauvet. The two methods have arrived at conflicting dates in the past, according to Clottes.
“You’ve got to keep a cool head and not go out of your way to be sensational,” he said, adding that both methods should be employed in further testing, where possible. Clottes is a former scientific adviser on prehistoric art to the French government and previously taught at the University of Toulouse. “You’ve got to cross-check.”
Radiocarbon dating was eschewed at El Castillo as that method doesn’t work when there isn’t any organic pigment, Pike said. Furthermore, only small samples can be dated using this method to minimize damage to the art, “magnifying the effects of contamination and resulting in larger uncertainties,” he said in the published paper.
The El Castillo artworks are “the oldest reliably dated paintings in the world,” Pike said on a conference call last week.
Uranium-series dating is also susceptible to inaccuracy, as some of the uranium in the calcite may have been washed out by later water flows, making samples appear older than they are, Clottes said. This led to discrepancies between results from the two methods to appraise cave paintings in Borneo in Indonesia, he said.
Such an effect was minimized as the scientists analyzed the top layers of the calcite, which would be younger than those underneath, Pike said. In Borneo, samples taken from powdery stalagmites may have yielded the differences in ages, while in Spain, only “hard, coherent” stalagmites were chosen, he said.
Pike’s team is continuing to gather more samples in Spain and France and will spend the next year analyzing them to determine whether the paintings were authored by Neanderthals.
“This is only the beginning of the process, not the end of the process,” he said in a phone interview. “This time next year, we’ll either be scratching our heads saying, it’s still as ambiguous as it ever was, or we’ll be able to come out with a fairly definitive statement.”