Mon. Sep 26th, 2022
A camera is held up with ancient rock art.

Mark Jones

Tens of thousands of ancient paintings adorn rock outcrops and shelters in the Kimberley region of Western Australia. In some locations, artificial layers on rock walls capture a range of styles and motifs that have changed over thousands of years. About the middle of that series, a style called Gwion depicts people in elaborate clothing and headdresses; the figures often carry boomerangs, spears, bags and ornaments.

“The paintings are like a diary to me and my people,” Ian Waina, a member of the region’s traditional Kwini owners, told the Australian Broadcasting Corporation. But neither the region’s traditional owners nor archaeologists know exactly how old the Gwion figures are or where they fit in the timeline compared to other types of rock art in the area. “Everyone wants to know how old the painting is,” Waina told ABC. “They just say this belongs to the ‘old people’. They know the stories, they keep those stories, but whose story does it belong to? Is it our older, older, older people?’

To pinpoint a more precise age, archaeologist Damien Finch of the University of Melbourne and his colleagues — including the land’s traditional owners, the Kwini and the Balanggarra Aboriginal Corporation — turned to an unlikely source: the remains of mud wasp nests.

Painted over insect ruins

Humans are not the only ones who leave behind archaeological remains. Around the Kimberley region, thousands of years of mud wasps have left their own little ruins: long-abandoned mud nests, weathered to flat stumps on the walls of sandstone rock shelters and outcroppings. In a few places, the red pigments of the Gwion figures are painted right over the weathered remains of old wasp nests.

When mud splatters scoop up material to build their nests, it often includes bits of charcoal from nearby wildfires, which archaeologists can use to radiocarbon date the nest. And Finch and his colleagues are using that as a way to narrow the age of the rock art itself, which has been challenging so far.

Ado French, from one of the local traditional owners' families, in front of some Gwion rock art figures.
enlarge Ado French, from one of the local traditional owners’ families, in front of some Gwion rock art figures.

Mark Jones

“For the older styles of Kimberley rock art, there’s nothing in the leftover pigment that we can date,” Finch told Ars. “The pigment is a red ocher, usually the iron oxide mineral hematite or jarosite, so it doesn’t contain any carbon that can be used for radiocarbon dating.” And uranium series dating, which has helped archaeologists date much older rock art elsewhere, only works in limestone caves where running water dissolves and deposits calcium carbonate — not in Kimberley’s open sandstone shelters.

Dating a cultural phenomenon

A nest built on top of a painting is likely younger than the painting, but a nest covered in pigment is likely older than the painting. In one spot, ancient people had painted a figure over the remains of a nest, and some time later, wasps built two more mud nests on top of the painting. Radiocarbon dating of those nests suggested the painting is 11,300 to 13,000 years old.

The other 20 paintings in the study had only one nest each, so Finch and his colleagues were given only a minimum or maximum age for each painting. But since the researchers wanted to know how long people had been using the Gwion style, rather than finding out the precise age of a painting, combining all those dates could still tell them something useful.

Twelve nests found atop petroglyphs suggested the paintings were younger than 12,000 years old. Meanwhile, nests among five other paintings suggested those paintings were at least 13,000 to 15,000 years old. Overall, these data give a rough idea of ​​how long early rock artists used the Gwion style before moving on to other styles and motifs. After some additional calculations, including factors such as the statistical reliability of each date, Finch and his colleagues concluded that the heyday of Gwion painting was 11,520 to 12,680 years ago.

There are always more questions

That’s considerably younger than archaeologists suggested in 1997, when a study (also involving mud wasp nests but using a different dating method) found that one painting by Gwion was at least 16,400 years old. But there is a limit to how much a single date can say about the history of rock art in the region. “Because it was only one minimum age, it didn’t tell us anything about how long the Gwion style was in vogue,” Finch told Ars.

One of the dates in the study also stood out as much older than the rest; a nest on top of a motif that is 16,600 years old.

“It’s possible that the motif is really 16,600 years old, but I’m not that confident,” Finch told Ars. “Radiocarbon dating is based on measurement of the radioactive isotope, carbon 14, and radioactive decay is a random process at the atomic level, so any 14C measurement depends on the statistical behavior of all 14C atoms present. So it is possible, but highly unlikely that a sample of something 12,000 years old, when measured, would produce a result that suggests it is significantly different from 12,000 years old.”

Probability calculations suggest that the sample’s date was only moderately reliable, but Finch and colleagues say it’s also possible that people in the Kimberley began painting Gwion motifs thousands of years before the height of the style. “Later this year, after I finish my PhD, there’s something I’ll try to see if we can confirm the date,” Finch told Ars. Ultimately, however, the questions can only be properly addressed with more data.

The big picture

The 21 paintings Finch and his colleagues studied are the largest specimen of Kimberley rock art ever dated, from an area of ​​100 kilometers (62 miles) of landscape. But they’re also just a drop in the ocean compared to the tens of thousands of paintings and galleries in the region, and the sampled paintings only cover a small portion of the area where Gwion motifs are found.

Finch and his colleagues have at least two more years of fieldwork ahead of them, and they are seeking permission from two other Aboriginal Corporations to work on their land.

“The Kimberley Rock Art Range is very complex, and there are many thousands of rock art sites, protected by their remoteness, in a region the size of Germany,” Finch told Ars. “It’s such a rich record of ancient human activity. We could easily work on this constantly for another 10 years and still have no answers to all the questions we have now, let alone new ones.”

Science Progress, 2020 DOI: 10.1126/sciaadv.aay3922 (About DOIs).

By akfire1

Leave a Reply

Your email address will not be published.