Ancient stone tools from an archaeological site on Sulawesi have pushed back the date of the earliest human occupation of the Indonesian island to at least 118,000 years ago.

The discovery, published today in Nature, overturns the view that humans first entered the island between 50,000 and 60,000 years ago as Homo sapiens dispersed out of Africa on the way to Australia.

Instead the finding suggests an ancient human species inhabited the island well before Homo sapiens arrived.

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Lead author Dr Gerrit van den Bergh, from the University of Wollongong, said it was likely this earlier inhabitant was related to the dwarf-sized hobbit (Homo floresiensis) — whose fossils were found more than a decade ago on the nearby island of Flores.

Dr van den Bergh, from the Center for Archaeological Science, who also worked on the Flores discovery, uncovered the open-air site at Talepu in Sulawesi's south-west in 2007. while surveying the area with Anwar Akib, from the local Cultural Heritage Department.

"This new road was cut in the area and I walked there with a local colleague [Mr Akib] and we stumbled upon this accumulation of stone artifacts in a gravel deposit," he said.

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Between 2009 and 2012 Dr van den Bergh and colleagues worked at the site excavating two trenches with the deepest reaching down 10 metres. More than 200 artifacts were recovered from the site.

However, it was only the development of new dating techniques by colleague Dr Bo Li at Wollongong University in 2011 that allowed them to date the site.

The luminescence dating technique estimates the burial date of the artifacts by determining the last time grains of feldspar — a silicate mineral — surrounding the tools were exposed to sunlight.

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This estimate was then supported by uranium dating of enamel on tooth fossils found at the site, which gave them a minimum age of 200,000 years old.

Dr van den Bergh said although the Nature paper put the date of earliest human occupation at 118,000 years ago, this was a "very conservative" estimate.

These stone artifacts were found scattered on a gravelly surface near Talepu.University of Wollongong

"Most artifacts occur in an interval bracketed by dates of 85,000 to 118,000 years, but three meters below the dated level of 118,000 years we still find stone artifacts," he said, adding that the animal fossils from the site that were dated at a minimum 200,000 years old were just 20 centimeters below these lowest artifacts.

"That tells us [the undated lower stone artifacts] are probably older than 200,000 years.

"It means it must have been archaic humans that made these stone tools."

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Cave art on Sulawesi shows modern humans (Homo sapiens) lived in Sulawesi around 40,000 years ago, Dr van den Bergh said.

"These modern humans must have encountered these archaic humans and what happened we don't know yet," he said.

He said the dense vegetation of the region made it difficult to find human fossils.

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In Flores they were now using 100 local laborers for two months each year to dig up earth in the hope of finding more human fossils.

Dr van den Bergh said it was likely they would take the same approach in Sulawesi.

He said the team's "working hypothesis" was that based on the sea current patterns in the area the ancestors of the hobbit (Homo floresiensis) came from Sulawesi.

"We have now proven these pre-modern humans were on Sulawesi and the search for their fossil remains is now open."

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Colin Groves, Emeritus Professor from the School of Archaeology and Anthropology at the Australian National University, said the finding was "quite significant".

Professor Groves agreed with the researchers' hypothesis that an older human species had been on the island.

"Compared to both Java and Flores, the date of a little over 100,000 is quite recent — nonetheless, it does extend human occupation of Sulawesi well back, making it highly probable that we have here a human species that is not Homo sapiens," he said.

"Whether it is a remnant Homo erectus, a dwarf-sized species in the mold of Homo floresiensis, or a fresh, undiscovered species endemic to Sulawesi, is just a matter for speculation at the moment, but certainly it is a very exciting prospect."