The discovery pushes back the technological advance to between 45,000 to 49,000 years ago, and coincides with the arrival of people in Australia, ABC Australia reported on Wednesday.
The fragment is 10,000 years older than the previous oldest known fragments found in northern Australia in 2010.
Although much older “hand axes”, usually made of flint, have been found across Europe and Africa – one well-known example found on a Norfolk beach is thought to be 700,000 years old – those were very different tools.
Archaeologists said the original axe would have been hafted – meaning it was made with a handle attached.
Professor Sue O’Connor, who discovered the fragment, said the world’s oldest known examples of hafted axes were all found in Australia.
“In Japan such axes (also) appear about 35,000 years ago. But in most countries in the world they arrive with agriculture after 10,000 years ago,” O’Connor, from the Australian National University School of Culture, History and Language, said.
She found the thumbnail-sized fragment in the early 1990s at Carpenters Gap – a large rock shelter in Winjana Gorge National Park – one of the first sites in Australia known to be occupied by modern humans.
In 2014, while O’Connor was re-examining the objects dug out of the site, she identified a possible polished axe fragment and approached professor Peter Hiscock of the University of Sydney to help verify the find.
The axe fragment was found in the same layer of sediment as a charcoal sample that was radiocarbon dated to 48,875-43,941 years old.
Professor Hiscock said these early innovations helped create cultural differences between groups.
“(The axe) is perhaps a material signal of cultural variations in the ancestors of Aboriginal people,” he said.
The findings appeared in the journal Australian Archaeology.