These ancient images were first reported more than half a century ago, but there had been no prior attempts to date them.
Scientists determined the age of the paintings by measuring the ratio of uranium and thorium isotopes in small stalactite-like growths, called ‘cave popcorn’, which had formed over the art.
Using this high-precision method, known as U-series dating, samples from 14 paintings at seven caves were shown to range in age from 39.9 to 17.4 thousand years ago. As the cave popcorn grew on top of the paintings the U-series dates only provide minimum ages for the art, which could be far older.
The most ancient Sulawesi motif dated by the team, a hand stencil made at least ~40 thousand years ago, is now the oldest evidence ever discovered of this widespread form of rock art. A large painting of a female babirusa also yielded a minimum age of 35.4 thousand years, making it one of the earliest known figurative depictions in the world, if not the earliest.