Pettitt and his archaeologist colleagues Sergio Ripoli, of the Universidad Nacional de Educación a Distancia in Madrid, and Paul Bahn, an independent expert on cave art, first discovered a small number of the carvings in April 2003 in caves known to have been inhabited before the end of the Ice Age.
The researchers described their initial find in the June 2003 issue of the archaeological journal Antiquity.
Other archaeological artifacts, such as figures and needles carved from bone, had previously been found at Creswell Crags. The objects, which dated to 12,000 to 13,000 years old, prompted Pettitt and his colleagues to scour the site for cave art.
The team's discovery of the carvings was widely reported in the media last year as the only Paleolithic cave art ever known from the U.K. Most other ancient British rock art is 8,000 years more recent than the art at Creswell Crags and is found on open rock faces.
Pettitt said his team used "stylistic comparison" with continental cave art and carbon dating of artifacts found at Creswell Crags to set a rough date for the art last year.
However, co-workers at Oxford University are now completing what's known as uranium-series dating. This type of dating, which measures the rate of decay of isotopes of uranium, is a useful method to date artifacts that contain no carbon and cannot be dated with more common radiocarbon dating methods.
The soon-to-be-released results will verify the estimated date of the cave art, Pettitt said.
Slow-growing stalactites and other mineral aggregations, which have built up on the surface of some of the carvings, were already an indication of the art's prehistoric provenance.
Some experts have argued that cave paintings are quickly degraded in the damp British climate.
Jon Humble is an inspector of ancient monuments with the government conservation body English Heritage, based in Northampton. He suggests that some experts were too quick to dismiss the possibility that lasting art from Paleolithic peoples could be found in Britain.
"There had been a psychological barrier to the existence of cave art in Britain but never a satisfactory explanation as to why there was none," he said.
The spectacular discovery at Creswell Crags now firmly places Britain on the cave-art map, Humble said. "The people who lived at Creswell Crags 13,000 years ago have quite literally carved out its place in prehistory, the present, and indeed the future," he said.
The carvings were not discovered sooner because they are nearly impossible to discern. Over the years the carvings have weathered drastically and are poorly lit.
"Now we know what to look for," Pettitt said. "I suspect there's a lot more British cave art out there to be found."
Prior to the discoveries at Creswell Crags, only two previous examples of Paleolithic British cave art had been reported. One was revealed to be a hoax, the other a false alarm.
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