it seems the theory is more disputed than i remember, so lets say around 5000 years ago there was perhaps significant indian introgression into aborginal genetics (as per article above), the introduction of new tools, the arrival of the dingo (speculated by some to be introduced by these indian peoples) and the spread of this language family from a small progenitor language to the dominant language on the continent. So something significant was happening at that time. There are other hints there couldve been previous waves of new peoples from art and so on (these are disputed, from memory). The story of the aboriginals will wind up being more complex and interesting than "showed up 60,000 years ago and were unchanged until the first fleet".