When lost Australian rancher Joseph Bradshaw stumbled across dancing, mulberry-colored figures painted on a rock shelter in the northwestern Kimberly region in 1891, he was mesmerized: They looked like no rock art he had seen before. Since then, the slender, detailed figures—now known as Gwions—have puzzled archaeologists, who didn’t know when they were painted or by whom. Now, scientists have used tiny specks of charcoal in fossilized wasp nests to come up with a new date for the paintings: 12,000 years ago.
“It’s fantastic,” says University of Wollongong geochronologist Richard “Bert” Roberts, who wasn’t involved in the work. Two decades ago, he used the nests to date the Gwions using a different technique; the new dates, he says, are solid. “Until now, we’ve been struggling.”
Dating the ancient works of art is hard for many reasons. The thousands of figures—which feature exquisitely detailed headdresses, tassels, boomerangs, and spears—were painted on rock shelters with mineral ochres that simply aren’t datable. Stylistically, the paintings are very different from nearby Wandjina art, characterized by spirit figures with huge dark eyes that are part of a mythology still embraced by today’s Aboriginal people. The charcoal often used for the Wanjina eyes allows for radiocarbon dating and puts the age of these paintings at up to 5000 years. But the Gwion palette did not appear to include charcoal.
To overcome that problem, Roberts and colleagues had turned to scores of ancient wasp nests speckled across the rock faces. Like the artists, mud wasps are partial to rock shelters, and they built some nests directly on top of the paintings—meaning the paintings are older than the nests. Using an optical technique that measured how long quartz sand grains had been buried inside, Roberts and colleagues dated a single large nest, and determined that the painting under it was more than 17,000 years old. The only problem: The technique could be used to date only large nests whose contents hadn’t been exposed to the Sun. And some researchers were skeptical the nest and painting could be linked. Roberts concedes: “In the ’90s, we barely knew what we were doing.”
Two decades later, Melbourne University Ph.D. candidate Damien Finch wanted to see whether he could date the art using a multitude of smaller nests that had been exposed to the Sun. He discovered that, along with sand grains, the wasps inadvertently deposited tiny specks of charcoal into their mud nests—which means that the nests, and therefore the paintings, could be dated by radiocarbon.
To understand how the carbon got there, Finch observed modern-day mud wasps over five field seasons. He identified other sources of carbon—such as ash deposited by nearby fires—and figured out how to expunge that from the ancient nests. Then, he dated the remaining carbon and verified that his method works, in work published in 2019.
For the current study, Finch and colleagues applied their method to wasp nests from 21 paintings at 14 different rock shelters. In 13 cases, the nests lay on top, making the paintings older than the nests. In six cases, the nests lay beneath, making the paintings younger than the nests. One painting had two overlying nests plus an underlying nest, allowing the researchers to reliably bracket the age of the Gwions for the first time: 12,000 years ago, give or take 500 years. That means, Finch says, the Gwion style lasted in the area for just a short period—1000 years or less.
That period coincides with the rapid ending of an ice age, when rising seas inundated northern Australia and shrank the lands of the Kimberley region by half. The resulting chaos displaced populations, and it may help explain why the Gwion artists focused on clan dynamics and ceremonies in their paintings, Finch says. The new dates also help dispel old notions that the Gwion artists were members of a non-Aboriginal group.
For Ian Waina, an Aboriginal guide and traditional custodian of the Balanggarra land where the Gwions in this study were found, the dates are welcome. “I believe in learning two ways, telling my stories and also telling tourists about the science. When they ask about the dates, I just say older than me and you. Now, I have a date.”