Australia's Aboriginal population is said to be the oldest continuing civilization on Earth – but just how old is that? It's currently believed that Aboriginal ancestors made their way to Australia as long as 65,000 years ago, but new evidence uncovered at a dig site in the continent's southeast may push the timeline back much further. If the site does turn out to be human-made, it suggests that people have been living in Australia for as long as 120,000 years.

The place of interest, known as the Moyjil site, is located in the city of Warrnambool, Victoria. Archaeologists have been investigating the area for over a decade, and the basis for these extraordinary claims is a mound of materials including sand, seashells and stones.

That might not sound like much, but the scientists suggest this is what's known as a midden – essentially, an ancient landfill. The remains of fish, crabs and shellfish have been found in the mound, which may be all that remains of long-eaten meals, while charcoal, blackened stones and other features may be all that's left of ancient fireplaces.

But the really intriguing part of the site is its age. If Moyjil does turn out to be a human site, it could force us to rewrite not just the history of Australian occupation but our understanding of human migration worldwide.

""What makes the site so significant is its great age," says John Sherwood, an author of the study. "Dating of the shells, burnt stones and surrounding cemented sands by a variety of methods has established that the deposit was formed about 120,000 years ago. That's about twice the presently accepted age of arrival of people on the Australian continent, based on archaeological evidence. A human site of this antiquity, at the southern edge of the continent, would be of international significance because of its implications for the movement of modern humans out of Africa."

But there are quite a few caveats to these claims. For one, there's every chance that the mounds aren't middens at all, but natural formations of some kind. Definitive proof of human occupation from that era, such as tools or bones, have yet to be found.

On top of that, it doesn't quite make sense within the current narrative. Genetic studies have shown that Aboriginal people only split off from other human populations about 75,000 years ago, after their ancestors migrated out of Africa, through Southeast Asia into Australia.

The oldest known definitive proof of humans on the continent are artifacts dated to 65,000 years ago, found in Kakadu National Park, along Australia's northern coast. This makes sense, given it's close to the islands the people were thought to have used to cross over.

But the Moyjil site is on the complete opposite side of the continent, and it's hard to believe humans appeared that far south, at a time when they were otherwise believed to be more or less restricted to Africa. Humans aren't thought to have even entered East Asia before about 100,000 years ago.

The researchers acknowledge the weight of the claims, and say they're working to continue examining the Moyjil site for further evidence of human occupation, and hope others will do the same.

"We recognize the need for a very high level of proof for the site's origin," says Sherwood. "Within our own research group the extent to which members believe the current evidence supports a theory of human agency ranges from 'weak' to 'strong.' But importantly, and despite these differences, we all agree that available evidence fails to prove conclusively that the site is of natural origin. What we need now is to attract the attention of other researchers with specialist techniques which may be able to conclusively resolve the question of whether or not humans created the deposit."

The research was published in the journal Proceedings of the Royal Society of Victoria.