(Zilhao discounts recent dates from Germany of up to 43,000 years ago.) Other researchers praise the study, but are cautious about concluding that Neandertals were cave artists.
"Excellent work," says geochemist Henry Schwarcz of Mc Master University in Hamilton, Canada, although he notes that daters can't say how much time passed between the creation of the art and the formation of the calcite layer.
And a few researchers say that the study argues for the slow development of artistic skill over tens of thousands of years.
U-series dating takes advantage of the fact that calcite, the form of calcium carbonate in stalactites and stalagmites, contains trace amounts of radioactive uranium-238, which decays to form atomic elements including radioactive thorium-230.
The dating of the Spanish caves leaves many gaps in a supposed sequence of increasing stylistic complexity, say archaeologists Iain Davidson of the University of New England in Armidale, Australia, and Nicolas Teyssandier of the University of Toulouse.
Higham says that "more work is required," but adds that the U-series technique may now allow testing of such hypotheses.
Dating expert Thomas Higham of the University of Oxford in the United Kingdom calls it "a very convincing study," adding that "it is just possible that a Neandertal hand was involved," in making the red disk.
But he still thinks it most likely that modern humans made the art, because the dates still correspond most closely to the time when was first entering Europe.