These methods — some of which are still used today — provide only an approximate spot within a previously established sequence: Think of it as ordering rather than dating.
Abstract Until recently, archeologists have generally agreed that modern humans arrived on Australia and its continental islands, New Guinea and Tasmania (collectively, Greater Australia), about 35,000 to 40,000 years ago,1 a time range that is consistent with evidence of their first appearance elsewhere in the Old World well outside Africa.2,3 Over the past decade, however, this consensus has been eroded, first by dates of 50,000 to 60,000 years from two sites in Arnhem Land and then, dramatically, by dates of 116,000 to 176,000 years from a third site on the eastern margin of the nearby Kimberley region.
From this discussion of the dating of Australian sites.
It’s entirely possible that humans were in Oz at this time, as there’s some evidence of contemporary occupation in Asia (Luijiang, at 68,000 years old).
Layers of rock build one atop another — find a fossil or artifact in one layer, and you can reasonably assume it’s older than anything above it.
Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.