The Toba super-volcano eruption took place 74,000 years ago and wiped out humanity over a large region of SE Asia – but there were some survivors. The traditional, single, out-of-Africa narrative puts the expansion wave beginning after the Toba eruption. My preferred narrative is of multiple waves out of Africa and into Arabia long before the Toba eruption and the main post-Toba expansion being from Africarabia. This narrative then includes admixture and assimilation of survivors from pre-Toba waves of expansion who were found along the way. Peoples from pre-Toba expansions who had settled in SE Asia would probably not have survived the eruption. Some of the pre-Toba peoples survived in isolated areas of India and points west and were mainly assimilated by later post-Toba waves.
The theory has been that it was post-Toba waves of humans which reached Australia around 40,000 years ago at the earliest. But evidence is emerging that humans were in Austalia at least 65,000 years ago. Distinctive stone tool assemblages including grinding stones, ground ochres, reflective additives and ground-edge hatchet heads have been found in Madjedbebe, a rock shelter in northern Australia and dated to 65,000 years ago (stratigraphic and optical dating).
That would suggest that the first human Australians came either directly from a pre-Toba expansion or post-Toba from peoples in SE Asia who had themselves oioginated from a pre-Toba expansion.
Clarkson, et al, Human occupation of northern Australia by 65,000 years ago, Nature 547, 306–310 (20 July 2017), doi:10.1038/nature22968
Abstract: The time of arrival of people in Australia is an unresolved question. It is relevant to debates about when modern humans first dispersed out of Africa and when their descendants incorporated genetic material from Neanderthals, Denisovans and possibly other hominins. Humans have also been implicated in the extinction of Australia’s megafauna. Here we report the results of new excavations conducted at Madjedbebe, a rock shelter in northern Australia. Artefacts in primary depositional context are concentrated in three dense bands, with the stratigraphic integrity of the deposit demonstrated by artefact refits and by optical dating and other analyses of the sediments. Human occupation began around 65,000 years ago, with a distinctive stone tool assemblage including grinding stones, ground ochres, reflective additives and ground-edge hatchet heads. This evidence sets a new minimum age for the arrival of humans in Australia, the dispersal of modern humans out of Africa, and the subsequent interactions of modern humans with Neanderthals and Denisovans.
My preferred narrative has at least three waves leaving Africarabia, starting perhaps around 120,000 years ago.