Thursday 6 February 2020

Mud wasps used to date Australia's aboriginal rock art

By Jonathan Amos
BBC Science Correspondent

5 February 2020

All the research has been conducted with the active participation of traditional owners

When the veteran telecoms engineer Damien Finch went on a three-week bush walk in Australia's Kimberley region, he became enthralled with its rock art.

On his return home, he tried to find out more about these enigmatic aboriginal paintings and engravings.

"I couldn't believe how little was known about them; we didn't even know how old they were," Damien said.

"It seemed disrespectful that scientists hadn't studied this stuff more; it was downplaying the importance of the culture," he told BBC News.

Now, 10 years on and in his 60s, Damien is putting that right.

He's approaching the end of his doctoral research on the topic, and in this week's Science Advances journal, has published his own efforts to age the Kimberley's so-called Gwion figures.

These feature finely painted human forms, often in elaborate ceremonial dress and carrying spears and boomerangs.

It was thought they were painted some 16,000 years ago, but the University of Melbourne investigator has been able to show the likely age is nearer in time - at about 12,000 years ago.

Dating rock art is really hard. Aboriginal artists use iron oxide pigments (ochre) which contain no organic material and are therefore resistant to any radiocarbon analysis.

Damien has got around this by studying instead the scraps of organic matter stuck on top of and underneath the paintings.

And for this, he's working with wasps. In particular, the ones that build nests out of mud. There's a wide group of these.

Some will enclose their prey - such as a paralysed spider or caterpillar - inside an earthen box. Before sealing the lid, the wasps lay an egg on the unfortunate victim. The developing larva then consumes the immobile spider or caterpillar, eventually digging its way out of the nest as an adult to carry on the cycle.

From Damien's point of view, when the female wasp gathers her mud supplies she inevitably picks up fragments of charcoal from the Kimberley's fire-prone landscape. And this charcoal can be radiocarbon dated.

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