El Castillo Cave in Cantabria on Spain’s northern coast was one of the UNESCO World Heritage Sites investigated for the study. The earliest dates were a minimum of 40,800 years ago for a red disk, 37,300 years for a hand stencil, and 35,600 years for a club-shaped symbol. The red disk is at least 4,000 years older than anything previously found in Europe and arguably the oldest cave art anywhere.
These early dates have sparked an interesting debate. The paintings are from the transition period between Neanderthals and the arrival of modern humans. No cave art has been firmly attributed to the Neanderthals and scholars have long debated the level of their intelligence.
Researchers used uranium-series disequilibrium dates of calcite deposits overlying art in eleven caves to determine the dates. Like radiocarbon dating, this technique measures the change in radioactive isotopes. Unlike the more common radiocarbon dating technique, however, which studies the half-life of carbon 14, this technique studies the rate of decay of uranium 234 into thorium 230, a process that happens at a precise rate. It can date calcite up to 300,000 years old.
Very thin films of calcite were sampled from just above the paintings. Being on top of the paintings, they are younger than the art, thus the paintings could be centuries older than the minimum dates given.
The results have been published in the journal Science. Meanwhile, the team is sampling more cave art in the hope of finding even earlier dates.