> "It’s a painting on a rock," he says. "You can never be completely sure who put it there, that it wasn’t some joker in the 1960s. But it’s likely that the ima

> "It’s a painting on a rock," he says. "You can never be completely sure who put it there, that it wasn’t some joker in the 1960s. But it’s likely that the image is authentic: there are much older paintings, produced with what seems to be the same iron oxide pigments, nearby." ...so how do they know that those other paintings are not from recent times?