A debate over the dating of prehistoric cave art has resurfaced after a French researcher challenged several widely publicized age estimates linked to some of the world’s oldest known paintings and hand stencils. The criticism focuses on uranium-thorium dating, often called U-Th dating, a method used to estimate the age of calcite layers formed over cave paintings.
In recent years, researchers working in caves across Spain and Indonesia reported increasingly older dates for prehistoric art. Among the most discussed examples are hand stencils from Sulawesi in Indonesia dated to about 67,800 years ago and paintings in Spanish caves dated to roughly 65,000 years ago. Those Spanish dates drew attention because they suggested Neanderthals created symbolic art long before modern humans entered Europe.
Georges Sauvet, a researcher at the Center for Research and Studies of Prehistoric Art in France, argues that many of these dates could be older than the artworks themselves. In a recent paper published in AOJ of Histoarchaeology and Anthropological Exploration, he warned that researchers are accepting extreme ages too easily in what he described as a growing race to identify the oldest rock art ever found.
U-Th dating works by measuring the radioactive decay of uranium trapped inside calcite deposits. When water flows through limestone caves, thin layers of calcite slowly form over paintings and engravings. These layers absorb uranium from groundwater. Over time, uranium-234 decays into thorium-230. Scientists estimate the age of the calcite by measuring the ratio between the two isotopes.
The method became important because many cave paintings were made with ocher or carved directly into rock, leaving little or no organic material suitable for radiocarbon dating. A calcite crust formed above a painting gives researchers a minimum age for the art beneath it.
The problem, according to Sauvet, is that the technique assumes the calcite remained chemically stable after formation. In many caves, water continues moving through the mineral layers for thousands of years. This process removes uranium from the calcite and changes the isotope ratio. When uranium leaks out, the samples appear far older than they are.
Sauvet pointed to several examples where U-Th results conflict with other dating methods. At Nerja Cave in southern Spain, one calcite layer covering a charcoal mark produced a U-Th age of nearly 119,000 years. Yet radiocarbon dating of the charcoal itself placed the drawing at around 19,000 years old. Radiocarbon dating of the calcite layer produced an age closer to 14,000 years.
He also highlighted unusual results from Indonesia. At Leang Balangajia in Sulawesi, an outer calcite layer yielded an age roughly 7,800 years older than the layer beneath it, even though the outer layer should have formed later. Sauvet argues that such reversals point to uranium loss and an “open system” rather than a stable one.
Another concern involves the mineral composition of cave deposits. Calcite and aragonite, two forms of calcium carbonate, behave differently during uranium dating. Aragonite absorbs much more uranium than calcite. When aragonite later changes into calcite, uranium is released and becomes easier to wash away. Sauvet believes this process may explain some unusually old dates reported in Spanish caves such as La Pasiega and Ardales.
The disagreement reaches beyond chemistry and geology because the dates influence ideas about human evolution and symbolic behavior. If the Spanish cave paintings are truly older than 60,000 years, Neanderthals likely created them. If the dates are inflated, the evidence for Neanderthal art weakens considerably.
Sauvet argues that future studies should rely on multiple dating methods whenever possible. He recommends combining U-Th analysis with radiocarbon dating and detailed physicochemical testing of calcite samples before announcing record-breaking ages.
Despite the importance of his warning, some researchers disagree with his conclusions. They argue uranium-thorium dating still produces reliable ages when scientists carefully examine calcite layers and apply strict laboratory testing to limit the effects of uranium loss. Researchers continue working to improve dating methods and resolve the debate over the age of prehistoric cave art.
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