Canberra academic Stephen Munro was sifting through photographs on his computer at ANU when a simple image of an old shell caught his eye.
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Immediately, the School of Archaeology and Anthropology researcher knew he had found something special.
With that one photograph Dr Munro has discovered the earliest man-made engravings – and unlocked our understanding of the world's early humans.
The 500,000-year-old fossilised shell is at least four times older than engravings previously believed to be the world's oldest.
The discovery also puts the etched patterns in the hands of Homo erectus rather than Neanderthals or modern humans, turning an outdated understanding of our early ancestors' capabilities on its head.
"It rewrites human history," Dr Munro said.
"This is the first time we have found evidence for Homo erectus behaving this way."
Dr Munro was looking through more than 300 images of shells from Dutch natural history museum Naturalis when he noticed a zig-zag pattern on one mollusc.
He photographed the mollusc during a study trip in Europe in 2007. The man who discovered Homo erectus, Eugene Dubois, gathered the collection of shells from Java in the 1890s alongside a human skull and femur.
"I just immediately went, 'wow, this is really exciting, this is significant'. I could see immediately that they were man-made engravings," Dr Munro said.
"The generally accepted view is this type of pattern, this geometric engraving, is about 130,000 years or so ago. The minimum date we've got with this shell is 430,000 years."
But the significance of the shell engraving stretches beyond just age.
The location of the of find, Indonesia, is outside the traditional Homo erectus stomping grounds of Africa and Europe and puts the humble shell at the centre of research.
"It's a shell rather than a bone or a piece of stone. You dont often read about shells," Dr Munro said.
"People don't think of shells as being a natural food resource. They think of Homo erectus as running after antelope on the open plains.
"This is really an idea that's grounded in the past and has no real relevance to what Homo erectus was actually doing, which was probably foraging primarily around water and getting food not only from the land but from the water, including shells like this."
Dr Munroe hoped the discovery will encourage researchers to think outside the square when studying the habits of early humans – and perhaps find even older engravings.
"For too long all people have been interested in is the antelope and the horses," he said.
"Finding a shell clearly associated with Homo erectus may encourage people to look at those lines of evidence a bit more closely.
"These engravings don't stand out. It's possible that without the digital image it may not have been discovered. It's probable there are other collections in other museums that may date even earlier than this."
