Thanks to a new dating technique, a rock painting found in the Leang Karampuang cave in Indonesia has revealed its staggering age. The painting is at least 51,200 years old, making it the oldest trace of rock art known in the world. It probably depicts a hunting scene with sketched human figures surrounding a large boar-like animal, but it could also be a bear. The uranium series dating technique helps determine the age of cave art by analysing the mineral deposits that accumulate on the cave's walls over time. In limestone caves, dripping or flowing water leads to the formation of mineral deposits on top of the paint layer. These are the same deposits of material that form stalactites and stalagmites. These deposits naturally contain calcium carbonate and small amounts of other elements, even uranium, a radioactive element that over time turns into different elements, such as thorium. Using a laser beam, the researchers made precise measurements in each layer of mineral deposited on the figure.
By comparing the ratio between the amount of uranium and that of thorium, scientists can calculate an age proportional to the time it took for thorium to form. That is, knowing that a certain amount of uranium transforms into thorium in a certain amount of time, by measuring how much of the former and how much of the latter element is present in a sample, it is possible to establish with a good level of accuracy the age of the source rock, layer by layer.
