We recently returned from a brief holiday in Darwin (follow this link). Interesting questions raised at the Darwin Museum and by the Warradjan Cultural Centre at Kakadu are where the Aboriginal people came from; how they got to Australia; and when.
Recent anthropology and archaeology seem to present contradictions and it seems to me that all these questions are controversial.
As I have mentioned in several other articles on this website, during the period of repeated glaciations called the Pleistocene (from around 2.5 million to about 12 thousand years ago) sea levels varied over a wide range. This was caused by the northern ice sheet repeatedly re-forming and melting; due to perturbations in the Earth's spin and orbit.
During the last period of low sea level, present day mainland Australia; New Guinea and Tasmania formed a single land mass, known to geographers and anthropologists as Sahul (Australasia), with a much extended coastline; just as Java; Sumatra; and Borneo; formed part of the Malay peninsular; incorporating the present gulf of Thailand; the Philippians and Indonesia; known as Sunda (Asia).
The ocean barrier that still separated these land masses accounts for the unique Australasian flora and fauna. This distinct change in biology is know as the Wallace Line. It was first identified by British naturalist Alfred Russel Wallace, Darwin's contemporary and the co-author of the theory of natural selection. The line provided strong supporting evidence for their joint paper to the Royal Society. At its narrowest, during the last glacial maximum, the ocean barrier was around 30km. As the sea rose Tasmania was cut off from the mainland; Australia was separated from New Guinea; and Indonesia and the Philippines became archipelagos.
Homo Sapiens Sapiens (modern man) was preceded in the region by Homo erectus. But he has been thought incapable of boat or raft construction and therefore of a sea navigation over, perhaps, swimming distance. So Sahul is thought to have been initially populated by modern humans; capable of deliberately or accidently crossing the reduced ocean barrier by boat or raft.