In recent years, researchers across the world have been publishing increasingly older ages for prehistoric rock art. Among the headliners is a painting of a warty pig in Indonesia that reportedly dates to 51,000 years ago and a hand stencil that researchers claimed was an eye-popping 67,800 years old.

Most of these dates have been determined by measuring the radioactive decay of some versions, or isotopes, of uranium into thorium ‪—‬ a method called uranium-thorium (U-Th) dating. However, the validity of some of these dates has been called into question, with Georges Sauvet, a researcher at the Center for Research and Studies of Prehistoric Art in France, proposing that the method tends to overestimate the ages of dated samples.