In search of the world's oldest cave etching

I'M DRIVING across South Australia's featureless but iconic Nullarbor Plain when suddenly the red earth falls away into a black abyss. "Dramatic really is the word for it," says Keryn Walshe.

Fifty metres wide and 25 metres deep, the sinkhole is a gateway to the mysterious Koonalda caves.Walshe, an archaeologist from the South Australian Museum, is leading a group of researchers and members of the Mirning people, the traditional Aboriginal owners of the land, into the caves. It has taken us 6 hours to drive here, after flying in from Adelaide, the nearest city, 900 kilometres away.

We have come to see strange wall markings that may have been a tactile code left by flint miners during the last ice age. The mine might be among the oldest in the world, as may the markings. The flint has clearly been cut away in numerous places and worked into tools, and ash deposits from fires show people have been coming here for tens of thousands of years.

For the Mirning, the intrigue is deepened by stories of a fearsome snake called Ganba that lived in the caves, making the faint hissing sounds we can hear.

A ladder takes us down to the cave floor, which drops steeply away from us, transforming into a glorious cavern. We turn a corner and the last of the daylight disappears. "You better get a photo of that," says one of the researchers, pointing at a mound of rocks that reduces the space in front of us to a crevice. "Behind that is where the markings are."

Following us are Robert Zlot and Mike Bosse from the CSIRO Autonomous Systems Lab in Brisbane. They look undeniably silly, each holding what looks like a dangling jack-in-the-box. In fact, it's the world's most versatile 3D scanning device, named Zebedee after the children's TV character.

"Nobody thought it was possible," says Bosse, who created Zebedee with Zlot. Until now, 3D scanners needed an independent fix on their location - extremely difficult in environments like this where GPS doesn't reach and surveys are hard.

"The smarts are in the software," says Zlot. Zebedee figures out where it has been by comparing scans as it goes along. It can scan the entire cave in the time it takes us to walk around it, sweeping the surfaces as it flops on its spring.

And then we see the markings. Wavy parallel lines known as flutings swirl around the contours of the damp, powdery rock. Some seem made by fingers, others are sharper and appear scratched. They could have been made using the claw of a dead animal, sticks or flint, Walshe says. Confusingly, though, some may have been made by trapped animals.

No one knows what they signify. Walshe says they are not likely to be art, in any modern sense of the word. Since they are in pitch darkness, they could be tactile signs, telling ancient Aboriginal miners where to go or where the best flint was. "Or they could be something as simple as 'hey, I was here'," she says.

Zebedee's scans will be combined with photos taken by George Poropat, also from CSIRO. The scanner's software will recognise the surfaces in those photos to create a 3D model with 0.25-millimetre resolution.

"The flutings are saying something, as they are repetitive in style and placement," says Walshe. "Those who made the marks must have believed that others who saw them understood the meaning." With the 3D scans, the team will be able to measure them, look for patterns and share the images with specialists around the world. They will even try to figure out the demographics of the people who made the marks by trying to figure out the size of the fingers, Walshe says.

Squeezing through gaps so narrow we can't turn our heads, we come to some 6-metre trenches dug by archaeologists in the 1960s. "It's madness... They had to do this by candlelight," Walshe says.

She's visibly excited when she finds chunks of ash in the deep layers of the trenches. Researchers in the 60s dated human activity here to 31,000 years ago. Limited ash samples and assumptions about Aboriginal migration meant that wasn't accepted at the time, but there's evidence nearby of human activity as far back as 41,000 years ago. If Walshe confirms this earlier date, it would mean people migrated the length of the continent far faster than was thought.

After 7 hours, the cave has been modelled, samples collected and we start the long drive back to the nearest roadhouse. By the time we have unpacked the SUV, Bosse has already created an interactive 3D map of almost the entire cave.

That night the cave's mysteries remained, but the answers are waiting to be decoded by our modern-day tools.

Michael Slezak travelled with Inspiring Australia

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