HUMANS may have arrived in Australia 15,000 years earlier than we thought. Artefacts found in the north of the country suggest that the region was occupied 65,000 years ago – which raises all sorts of questions about how the country’s first inhabitants interacted with wildlife and what became of them.

Until recently, the oldest evidence of human occupation in Australia came from 50,000-year-old stone artefacts found in a rock shelter in the country’s north.

When was north Australia settled?

Now Chris Clarkson at the University of Queensland and his colleagues have found artefacts dating back 65,000 years in a different rock shelter – this one in Kakadu National Park in the far north of the country. The artefacts include fireplace remains, stone axes, grinding stones, ground plant matter and ground ochre – a type of red pigment commonly found in ancient rock art in northern Australia. Clarkson’s team calculated the age of the artefacts by dating charcoal and quartz grains buried in the same layer of sediment (Nature, DOI: 10.1038/nature22968).

Alan Cooper at the University of Adelaide is perplexed by the discovery, given that nothing so ancient is found anywhere else in Australia. “We know these people were fast movers – they moved very quickly from Africa to Asia to Australia,” he says. “So if they did arrive in northern Australia 65,000 years ago, why did they then just sit down and wait 15,000 years before spreading to the rest of the country?”

Adding to the mystery is the fact that it is unclear where the first Australians came from. The easiest route into Australia is via the chain of islands directly to the north, but there is little evidence that Homo sapiens was present on these islands much before 44,000 years ago, says Sue O’Connor at the Australian National University.

This is an evolving picture, though. For instance, there is some evidence that H. sapiens reached a more northerly island of South-East Asia – Luzon in the Philippines – 67,000 years ago.

O’Connor is also puzzled by the early humans’ wanderlust. Sea levels were substantially lower 65,000 years ago, making it easier to move between Asia, Australia and the islands en route. But humans still had to cross open water stretching for 80 kilometres to make it to mainland Australia, she says. “There’s no obvious reason like climate shifts to explain the rapid movement.”

An earlier arrival date for humans is also in line with arguments that our species is responsible for the demise of some Australian megafauna. Creatures including giant versions of birds, echidnas and wombats, and tree-dwelling lions went extinct about 45,000 years ago.

However, just because people co-existed with megafauna for 20,000 years doesn’t mean they were responsible for the extinction, says O’Connor.

“Humans may have had an impact through fire practices and hunting but there’s no solid evidence either way,” she says.

This article appeared in print under the headline “Earliest Australians are a prehistoric puzzle”