New excavations of a rock shelter near Kakadu National Park indicate humans reached Australia at least 65,000 years ago — up to 18,000 years earlier than archaeologists previously thought.

Key points: Date of site near Kakadu has been debated for nearly 30 years

Date of site near Kakadu has been debated for nearly 30 years Prior to this study many archaeologists believed humans arrived in Australia between 47,000 - 50,000 years ago

Prior to this study many archaeologists believed humans arrived in Australia between 47,000 - 50,000 years ago Excavation found a wealth of artefacts including ground-edge axes, grindstones, flints and ochre as well as evidence of fireplaces right through the site

Many scientists already accepted that the shelter, called Madjedbebe, was home to the earliest evidence of humans in Australia.

But now, sophisticated dating of sediments at the site confirms it is one of the most significant cultural and archaeological sites in the world.

Three axes from different layers of the site and a rectangular sharpening stone from the 65,000-year level. ( Supplied: Gundjeihmi Aboriginal Corporation/Dominic O'Brien )

Chris Clarkson from the University of Queensland said the new date would have a big impact on our understanding of when humans left Africa and moved through what is now South-East Asia.

"This site confirms, once more, that this is an incredibly important region — not only in Australia, but on the world stage, in terms of cultural heritage and understanding human origins," Dr Clarkson said.

Located 300 kilometres east of Darwin in Mirarr Country, the Madjedbebe rock shelter sits at the base of the Arnhem Land escarpment on a sandy plain.

Dr Clarkson said the discoveries, published today in the journal Nature, demonstrated very strong cultural continuity at the site across thousands of years.

The researchers uncovered a wealth of artefacts, including the world's oldest-known ground-edge axe head — one made by grinding rather than flaking.

"The fundamental aspects of technology, such as axes, grindstones and the production of ochre to produce art goes from the present right the way [back]," Dr Clarkson, who was the lead author of the study, said.

"It suggests there is a very, very deep continuity and connection between the people living in Kakadu today and probably those living there 65,000 years ago."

Landmark agreement with traditional owners

The Madjedbebe site, which sits within the Jabiluka mining lease outside the national park, is known for its rich art gallery of images depicting events right up to early contact with Europeans, including images of guns, wagons and ships on the back wall.

Mirarr traditional owner May Nango said she was worried about passing knowledge from the site onto the next generation.

Madjedbebe site custodian May Nango and excavation leader Chris Clarkson in the pit. ( Supplied: Gundjeihmi Aboriginal Corporation/Dominic O'Brien )

"This country belong to Mirarr, and even the kids too," she said.

"Try to show all them young kids too, so they can remember all from our old people that gave us this story."

"We like staying forever, we buried there too, we like to stay with our country, with our land."

Ms Nango said she wanted to make sure the site was protected.

"Stay normal, my country gotta stay normal like this, long time," she said.

"But now the balanda [non-Indigenous people] comes and cleaning up all them trees, everywhere digging."

Dr Chris Clarkson explains the excavation site to local rangers. ( Supplied: Gundjeihmi Aboriginal Corporation/Dominic O'Brien )

Excavation at the site was conducted under a landmark agreement between the Gundjeihmi Aboriginal Corporation representing the traditional owners, and the researchers.

Under the agreement, the Mirarr people have had a right to veto the excavation at any time, control over the artefacts and final say about findings announced about the site.

Justin O'Brien, CEO of the Gundjeihmi Aboriginal Corporation, said the agreement ensured the Mirarr people could have control over how the excavation was conducted.

"We said, okay, these are the conditions on which you come upon this country," Mr O'Brien told RN's AWAYE! program.

"That meant there was a spirit of cooperation from the start.

"When issues arose from the dig [the researchers] would quickly down tools. They would quickly call us. We would speak to the traditional owners and be out there and have a look directly."

Dr Clarkson said the agreement was one of the strongest agreements ever negotiated in Australia between traditional owners and archaeology teams.

"Aboriginal involvement, Aboriginal permission, Aboriginal rights over the excavation itself are very important in this kind of endeavour," he said.

Mirarr traditional owner May Nango (second the right) hopes to protect the site for future generations. ( Supplied: Glenn Campbell )

Rich evidence of human behaviour

The site was last excavated nearly 30 years ago. At that time it was thought to be between 50,000 and 60,000 years old. But these dates had been disputed by some archaeologists.

To settle the dispute, Dr Clarkson and colleagues returned to the site in 2012 and 2015 armed with more sophisticated technology and techniques.

The team uncovered artefacts in three bands of sediment corresponding to different ages — the lowest of which was around 2.6 metres below ground. This layer contained evidence of a fireplace and thousands of artefacts.

Along with the axe, the archaeologists found the oldest-known grinding stone in Australia, as well as stone points that may have been used as spear tips, and ochre crayons.

Early paints recovered from the site also contained the world's oldest-known use of reflective minerals such as mica.

"We found there was an incredible richness of evidence of wonderful human behaviour that we didn't really have indications of from earlier excavations," Dr Clarkson said.

The Madjedbebe rock shelter is the oldest-known site of human occupation in Australia. ( Supplied: Gundjeihmi Aboriginal Corporation/Dominic O'Brien )

Sand grains reveal age

Professor Zenobia Jacobs of the University of Wollongong used a combination of radiocarbon dating, and a technique called luminescence dating, which can tell when single grains of sand were last exposed to sunlight, to determine the age of the sediment surrounding the artefacts.

The results indicated the lower layers were around 65,000 years old, give or take about 5,000 years.

To make sure the dates were correct, Professor Jacobs sent four samples to the University of Adelaide for independent testing. The results were the same.

"That blind study made us feel very confident about … about the accuracy of the ages," she said.

Professor Peter Hiscock of the University of Sydney was one of the archaeologists who was sceptical about the dates presented nearly 30 years ago.

He said the new study had convinced him it was the oldest site in Australia, although he thought the date of 65,000 years was "optimistic".

"It certainly persuades me that people were there by 60,000 years — they could be there earlier — and that is really quite significant," he said.

Early Australians used innovative technologies such as ground-edge axes. ( Supplied: Gundjeihmi Aboriginal Corporation/Chris Clarkson )

He said he was cautious about pinning down an exact date as artefacts may have moved from the sediment they were originally in.

Professor Jacobs said there was a small amount of movement at the site of around 10 to 15 centimetres, but that was not enough to change the position of the artefacts.

"There is a lot of independent strands of evidence pointing to there being limited disturbance of the artefacts over time," she said.

A fresh look at the human journey needed

Professor Hiscock said the significance of this "great discovery" is what it tells us about Australia's first people and their journey out of Africa.

"The artefacts in this site are unambiguously the evidence for the time at which Homo sapiens reach Australia," he said.

He said the artefacts indicated the first Australians were able to quickly adapt to their new environment.

"What we are seeing is that from the moment people are arriving in Australia they are exploiting the landscape, they are creating artwork in their shelters, and they are inventing new kinds of technologies, such as ground-edge axes, which are older than anywhere else in the world," Professor Hiscock said.

"Probably that level of sophistication is the reason why they were able to move from Africa to Australia.

"What we don't know is when they left Africa."

Excavation leader Chris Clarkson examines a stone tool. ( Supplied: Gundjeihmi Aboriginal Corporation/Dominic O'Brien )

Palaeoanthropologist Michael Westaway of Griffith University agreed the "foundational" study would make scientists take a fresh look at that question.

He said the latest genetic evidence indicates that humans moved out of Africa about 72,000 years ago — although there is archaeological evidence they may have been in the Near East 110,000 years ago.

"It means that within several thousand years, Homo sapiens were in Australia," Dr Westaway said.

"That's a very rapid expansion across the globe."

Once they moved out of Africa, Homo sapiens bred with Neanderthals and Denisovans before moving into South-East Asia then into the supercontinent of Sahul — what is now New Guinea and Australia.

The new dates also indicate modern humans lived in the same region as the ancient, now extinct, Homo floresiensis aka 'the hobbit', for at least 15,000 years.

"So [this study is] a real shock to our understanding of modern human origins and dispersal in this part of the world."

Hear more about human evolution and this discovery on RN's Science Show, and the Indigenous perspective on RN's AWAYE!