When Did Humans Reach Australia?

At the height of the last Ice Age, sea levels were about 120 metres lower than today. Australia, New Guinea and Tasmania merged into a single continent that geologists call Sahul. Southeast Asia extended east into a shelf called Sunda. But no amount of falling sea level ever joined them. Between Sunda and Sahul lies Wallacea, a chain of deep-water islands, and crossing it always required at least 90 kilometres of open sea, with a stretch where the destination is not visible from the departure point.

Someone made that crossing, in numbers large enough to found a viable population, more than fifty thousand years ago. It is the earliest evidence of purposeful seafaring anywhere on Earth.

The 65,000-year claim

In 2017, Chris Clarkson and colleagues published excavations at Madjedbebe (formerly Malakunanja II), a rock shelter on Mirarr country in Arnhem Land. The lowest artefact-bearing layers — containing over 10,000 stone artefacts, ground ochre “crayons”, reflective mica, and the world’s oldest known edge-ground hatchets — were dated by optically stimulated luminescence to about 65,000 years ago.

The dating method is sound; the debate is about stratigraphy. Critics, notably Jim Allen and Jim O’Connell, argue that artefacts in loose sandy sediment can migrate downward through the deposit over millennia, ending up associated with sand grains older than they are. Supporters point to the tight vertical clustering of artefact types and the presence of intact features. The argument is unresolved and conducted in good faith on both sides.

What almost everyone accepts is the lower bound: at least 50,000 years, and probably a little more. Multiple independent sites across the continent cluster in the 45,000–50,000 range, which is difficult to explain unless people arrived somewhat earlier and then spread.

Lake Mungo

The most important Australian burials come from Lake Mungo in the Willandra Lakes, New South Wales — now a dry, wind-scoured basin, then a full freshwater lake system.

Mungo Lady (WLH1), found in 1968, was cremated, her bones then crushed and burned a second time before burial. At around 40,000–42,000 years old, she is the oldest known cremation anywhere in the world. Mungo Man (WLH3), found in 1974, was laid out on his back, hands crossed, and sprinkled with red ochre that had to be carried from at least 200 km away.

These are not casual disposals. They are ritual, they involve costly imported materials, and they are roughly contemporaneous with the earliest ceremonial burials in Europe. Both sets of remains were returned to the Willandra Aboriginal traditional owners — Mungo Lady in 1992 and Mungo Man in 2017 — and reburied on country.

What the genetics show

A 2016 study in Nature led by Anna-Sapfo Malaspinas sequenced 83 Aboriginal Australian and 25 Papuan genomes. The findings:

• Aboriginal Australians and Papuans descend from a single founding population that split from Eurasian lineages around 58,000–50,000 years ago.
• That population then diverged internally into Australian and New Guinean branches roughly 37,000 years ago — long before rising seas separated the two landmasses about 8,000 years ago.
• Aboriginal Australian populations then diversified across the continent and remained substantially structured for tens of thousands of years.

They also carry the highest Denisovan ancestry outside the Philippines — around 4%, with Papuans similar or higher. That means their ancestors met and interbred with Denisovans somewhere in island Southeast Asia on the way through, which is a startling thing to learn from a population whose Denisovan relatives are known mainly from a cave in Siberia.

The upshot: Aboriginal Australians represent one of the longest continuous cultural traditions on Earth, on the same continent, for at least 50,000 and perhaps 65,000 years.

And the megafauna?

Sahul had an extraordinary fauna: Diprotodon, a wombat relative the size of a rhinoceros; Thylacoleo, the marsupial “lion” with bolt-cutter premolars; Genyornis, a flightless bird twice the mass of an emu; Megalania, a monitor lizard perhaps 5 metres long; and short-faced kangaroos over 2 metres tall.

Most were gone by around 40,000 years ago. Whether humans, climate, or both are responsible has been argued for fifty years. Burnt Genyornis eggshell fragments in patterns consistent with cooking suggest direct human exploitation of at least one species. Others point to a long-term drying trend that would have squeezed large-bodied animals regardless. The current consensus leans toward humans as a significant contributing factor operating on populations already stressed by climate — the same shape of argument as for Ice Age extinctions elsewhere.

Why the crossing matters

Reaching Australia is the earliest hard proof that our species could plan a journey it could not see the end of. Whatever the craft was — bamboo raft, bark canoe, lashed logs — it has not survived, and probably never will. But the destination did, and so did the people who arrived.