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A cave on the island of Timor has given archaeologists a vital clue to the route taken by ancient humans when they first made their way to the Australian continent.

It is known from archaeological evidence in Australia’s Northern Territory that people were there at least 65,000 years ago. At this time, when sea levels were lower, Australia and New Guinea were part of a larger landmass known as Sahul.

Researchers believe there are two likely routes people could have taken from South-East Asia to Sahul. One is a southern route via Timor. Alternatively, Homo sapiens could have travelled via Sulawesi, an island to the north of Timor.

Now, at the Australian National University in Canberra and her colleagues believe they have found evidence ruling out the possibility that the first arrivals came through Timor.

In other locations on Timor, the oldest evidence of human occupation was less than 50,000 years old. Archaeologists were unable to look for older artefacts as, at all the other sites they studied, they hit bedrock rather than sediment layers that could potentially contain evidence of an earlier presence, says O’Connor.

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In 2019, her team dug a new pit at a cave called Laili, on the north coast of East Timor, and discovered a rich deposit of archaeological evidence including tens of thousands of stone tools, proving that humans had occupied the island for 44,000 years.

Crucially, however, this layer of occupation was underlain by sediments with no evidence of humans. This means it is likely that before 44,000 years ago, people were absent, says O’Connor.

“This is the first time in Timor that we have sterile, non-occupation layers below evidence of people’s presence,” she says.

O’Connor says such a clear boundary between no evidence of humans followed by tens of thousands of years of artefacts is called an “arrival signature”.

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The cave’s prominent location and access to resources gives the researchers confidence that it is unlikely to have been missed by any early humans travelling through the area.

“It’s a really, really big cave with a big flowing river in a braided floodplain and very close to the coast,” says O’Connor. “It’s a perfect place for people to establish an occupation base camp. You couldn’t find a more ideal setting.”

Because of the evidence that people were in Australia 65,000 years ago but not in Timor until 44,000 years ago, it means humans most likely migrated via the islands to the north, says O’Connor.

“Looking at the layers in Laili cave, it’s like ‘bang’ – you can really see clearly when the people arrive,” she says. “It was like a line had been drawn between the two layers – before people and after people. It was so clear.”

at the University of Western Australia says the case for a later date for the occupation of Timor is building. He says ancient Australians were not as isolated as was once believed and that there were probably multiple waves of migration to Sahul.

“I think an earlier northern route seems plausible. This is a highly significant site as, based on a broad suite of shellfish, fish, crustacea and other resources found in the cave, it shows there was a fully fledged maritime economy in place when Timor was settled.”