Archaeological Evidence
Until recently anthropology was based on 'digs' in places where remnants of bone or artefacts were found. In Australia these seemed to present contradictory evidence and raised as many questions as they did answers.
In contradiction to DNA based dating that suggests original arrival in the region around 40 thousand years ago, and repeated new arrivals since, archaeological dating of Aboriginal tools and art suggests that settlement may have happened as long as 90 thousand years before present.
This timing is in dispute in academic circles. Based on the above DNA evidence and archaeological finds in countries that must have been populated first, 90 thousand years seems to be far too early for modern humans to have arrived.
The oldest human remains in Australia found at at Lake Mungo in NSW date to around 40 thousand years ago. Initial mtDNA analysis found that this person was unrelated to present day Aboriginal people. But this has been claimed to be scientifically faulty and is dismissed by many in the field. Local people have since prevented any re-testing of the remains. Aboriginal supported research at Lake Mungo has since found footprints and hominin manufactured artefacts that have been dated to as early as 78 thousand years ago.
The dating of some objects could well be defective as radio-carbon dating of related organic deposits becomes less accurate after about 30 thousand years and other methods need to be used. Some dating methods that rely on the age of surrounding material or the depth at which artefacts are found, may be problematic if they were buried either by humans or reburied by some natural disturbance; like a flood.
But a verified very early date would strongly suggest that the artefacts found are not associated with modern humans at all but with another advanced hominin, possibly Denisovan; Homo erectus soloensis or Homo Floresiensis.
These earlier hominins certainly had a much longer time; and more periods of low sea level to reach Australia; but could they build boats; or rafts; or accidently get swept into the sea as a family? How did they get as far south as Java and Flores?