Aborigines have been in Australia for at least 40,000 to 60,000 years. The later time is still the main one given, but there is enough evidence to push that back to the earlier date, perhaps even to 70,000 years. What is intriguing is not where they came from, which is from Asia, but how they got to Australia.
The people in Asia that they most resemble are the original people of India. Although this is not universally accepted, I think they are the most likely ancestors. The peoples who now live in Southeast Asia between India and Australia were later arrivals, supplanting the original inhabitants. The most common assumption is that the Aborigines arrived via a land bridge, like the aboriginal Americans arrived from Siberia. Unfortunately, there was never a land bridge between Asia and Australia anywhere near a time when the Aborigines needed to have crossed (or since). Even at the most optimum, there were 150 miles of ocean that had to be navigated, and this was at a time long before early man took to the sea, before boats, before canoes, before rafts, before anything made to float on. At 150 miles, no land on the other side or loom of land is visible.
It is possible that by accident, a person clinging to a log could drift across to Australia, but even at the shortest distance of 150 miles, it would take many days, assuming a steady progress. One person is not enough; two are needed for procreation. But even that is a stretch. A scientist, whose work I read while still in Australia, writing on this problem, said that it would take a group of at least 27 or 28, for survival to be viable. That figure is the bare minimum. Is it possible that such a large group could have drifted across?
Actually, and here comes the speculation, it is possible, more than 28, possibly hundreds, but they were not drifting. They were washed over. This speculative scenario occurred to me while I was rereading Velikovsky’s Earth in Upheaval.
Velikovsky wrote Earth in Upheaval to counteract criticism that there was no hard evidence for major catastrophes in the past, as he postulated in Worlds in Collision, which was based on ancient records and mythologized remembrances of ancient peoples. The evidence he gathered for Earth in Upheaval does show massive catastrophes that not only suddenly wiped out large numbers of ancient animals, like mammoths, hippopotami, various predators, and so forth, all mixed up and smashed into crevices and caves, so suddenly that the food was undigested and grass being eaten was still between the teeth. Mixed in amongst them were also human remains. Errant boulders were pushed long distances, even uphill, and much, much more.
The part that I focused on was the evidence of vast tidal waves that swept over large areas of the world. There are no precise times for these, but the range of animals involved roughly match our years of interest. (Later in the book, he focuses on the last millennium BCE.) The cause for the tidal waves may have been some kind of cosmological ping-pong in our solar system, but the cause is not really relevant here. Such a huge tsunami could have swept enough survivors onto the Australian continent. In their new country, these new Aborigines would have found plenty of large game (assuming it survived), and a new environment to adapt to and gradually to make their own.
One final speculation can be made, assuming cosmological origins of the catastrophe. In Worlds in Collision, Velikovsky links the concept of dragons and the like to apparitions seen in the sky during planetary close encounters. For the aborigines, the Rainbow Serpent is the most important concept in their mythology. Is there a corresponding origin here with that of the dragons?
(To give a perspective on the time span involved, I should add that Aborigines were in Australia well before humans got to Europe.)