The basic questions about early European cave art—who made it and whether they developed artistic talent swiftly or slowly—were thought by many researchers to have been settled long ago: Modern humans made the paintings, crafting brilliant artworks almost as soon as they entered Europe from Africa. Now dating experts working in Spain, using a technique relatively new to archaeology, have pushed dates for the earliest cave art back some 4000 years to at least 41,000 years ago*, raising the possibility that the artists were Neandertals rather than modern humans. And a few researchers say that the study argues for the slow development of artistic skill over tens of thousands of years.
Figuring out the age of cave art is fraught with difficulties. Radiocarbon dating has long been the method of choice, but it is restricted to organic materials such as bone and charcoal. When such materials are lying on a cave floor near art on the cave wall, archaeologists have to make many assumptions before concluding that they are contemporary. Questions have even arisen in cases like the superb renditions of horses, rhinos, and other animals in France's Grotte Chauvet, the cave where researchers have directly radiocarbon dated artworks executed in charcoal to 37,000 years ago. Other archaeologists have argued that artists could have entered Chauvet much later  and picked up charcoal that had been lying around for thousands of years.
Now in a paper published online today in Science, dating expert Alistair Pike of the University of Bristol in the United Kingdom and archaeologist Paul Pettitt of the University of Sheffield in the United Kingdom, together with colleagues in Spain, applied a technique called uranium-series (U-series) dating to artworks from 11 Spanish caves. U-series dating has been around since the 1950s and is often used to date caves, corals, and other proxies for climate and sea level changes. But it has been used only a few times before on cave art, including by Pike and Pettit, who used it to date the United Kingdom's oldest known cave art  at Cresswell Crags in England.
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. By measuring the ratio of thorium-230 and uranium-238, daters can estimate how long ago the calcite was laid down.
Using a blade or an electric drill, the team took 50 small samples from calcite that directly overlay either paintings or engravings in 11 caves in northwest Spain. Because the calcite overlays the paintings, it must be younger than the art, and so yields minimum ages. In a few cases, the team also dated calcite underneath artworks, thus creating a "sandwich" that generated maximum and minimum dates.
The results, if correct, include the earliest ever reported date for cave art : A red disk from El Castillo Cave, on the Pas River in northern Spain, clocked in at a minimum of 40,800 years. The disk, part of a larger composition that includes dozens of other disks and some 40 stencils of human hands, could be older, depending on how soon after it was painted the calcite layer formed. Other early dates include 37,300 years for a hand stencil at Tito Bustillo Cave and 35,600 years for a club-shaped image at the famous Altamira Cave, whose artworks were previously thought to be only about 17,000 years old.
Forty-thousand years ago, Neandertals were still living in Spain, while modern humans were only just entering Europe. Thus co-author Joao Zilhao, an archaeologist at the University of Barcelona in Spain who has long championed Neandertals' symbolic and creative capacities , contends that there is "a strong probability of Neandertal authorship." He points out that Neandertals made jewelry and used ochre, and that the oldest known modern human fossils in Europe, from the site of Pestera cu Oase in Romania, are only about 39,000 years old. The earliest possible dates for archaeological artifacts associated with modern humans, in Spain, Italy, and France are about 41,600 years ago. (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 McMaster 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. 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 Homo sapiens was first entering Europe. Archaeologist Nuno Bicho of the University of Algarve in Portugal agrees that "the new data seem to fall a bit short of confirming [the] idea," that Neandertals were artists.
The team also says that the new work has big implications for cave art elsewhere in Europe, including the magnificent paintings at the Grotte Chauvet, which have long served as the chief evidence for early humans' precocious artistic talents. Since the Chauvet art was discovered in 1994, many researchers have seen it as evidence that modern humans arrived in Europe from Africa ready, willing, and able to create sophisticated paintings that rival those of much later caves , such as Lascaux in southern France. The team argues that the new dating, along with similar dates from sites such as Abri Castanet in France, where archaeologists recently dated depictions of female genitalia to at least 37,000 years ago , suggests that the earliest European artists "were less concerned with animal depictions" and more interested in simpler motifs such as "red dots, disks, lines, and hand stencils," as they put it in the Science paper.
"There is an emerging picture of the earliest cave art being largely nonfigurative," says Pettitt, who has long challenged the Chauvet dates as too old. "Chauvet is the only example which apparently defies this rule." He concludes that an "evolutionary model" of art, from simpler motifs to sophisticated animal and human figures, better fits the data and that the Chauvet dating is probably wrong.
The French dating team at Chauvet is disdainful of such a conclusion. "The dating at Chauvet has been confirmed over time" by numerous studies, says Gilles Tosello, an archaeologist at the University of Toulouse in France who has worked at the site since the late 1990s. The Pike team has not taken into account several potential problems with U-series dating, adds Helene Valladas of the Laboratory of Climate and Environmental Sciences in Gif-sur-Yvette, France, who led the dating at Chauvet. She says it's possible that some of the uranium in the calcite has been washed out by later water flows, which would increase the thorium/uranium ratio and make the ages seem older than they really are. Valladas says she and her colleagues encountered just such problems when they attempted to compare and crosscheck U-series and radiocarbon dating results from prehistoric cave paintings in Borneo  back in 2003.
Other researchers say the jury is out on whether prehistoric European cave art became more sophisticated over time. 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. Pettit and Pike say they stand ready and eager to date other sites, including Chauvet.
But that's an invitation unlikely to be forthcoming very soon. Tosello, speaking for himself and not officially for the team, calls Pettitt "anti-Chauvet," and adds that it is "not acceptable" for other scientists to "dictate" sampling strategies to the Chauvet team.
Nevertheless, Tosello says that he can envision the new technique being used at Chauvet if and when it has proven itself. And given the apparent success of Pike and his colleagues in coming up with new dates for the Spanish caves, U-series may eventually change the landscape of European cave art.
* All dates in this story have been calibrated for their method and are expressed in actual calendar years.