Evidence for human activity on island in ancient mega-lake
Lake Mungo is the largest of a series of 19 now dried up lakes making up the Willandra Lakes system. The region is a World Heritage Site covering 2,400 sq. km (925 sq. miles) in southwest New South Wales, about 1,000 km (620 miles) west of Sydney. The water levels in the lakes remained high until 45,000 years ago and then began to decline. They dried up completely 22,000 years ago, and have remained dry ever since. However, a recent survey has shown that 24,000 years ago, Lake Mungo underwent a sudden massive filling episode, increasing its depth by 5 m (16 ft.) and its volume by 250 percent. Lake Mungo became linked to its neighbour, Lake Leaghur, at two overflow points, so creating an island in between.
Humans arrived in the Lake Mungo region at least 20,000 years before the mega-lake phase. The expansion of Lake Mungo would have substantially affected mobility, forcing people to skirt the mega-lake. However, the presence of hearths and stone artefacts on the island suggests that they repeatedly crossed the inflow channel, taking stone tools and hunting equipment with them. While they could have swum, using bags to carry tools, it is likelier that they used boats.
This implies a highly flexible response to the sudden change in conditions, and possibly a re-discovery of boat technology. While Aboriginal Australians must have used boats to reach Australia in the first place, there is a lack of evidence for pelagic fishing and navigation to offshore islands around the Australian coast until a few thousand years ago. It has accordingly been assumed that watercraft technologies were abandoned after initial arrival and dispersal across Australia. If boats were used to cross Lake Mungo during its expanded phase 24,000 years ago, then this represents the revival of a technology which had apparently been abandoned over 20,000 years earlier, and at a location well inland and far from any major navigable rivers.
Fitzsimmons, K., Stern, N., Murray-Wallace, C., Truscott, W. & Pop, C., The Mungo Mega-Lake Event, Semi-Arid Australia: Non-Linear Descent into the Last Ice Age, Implications for Human Behaviour. PLoS One 10 (6), e0127008 (2015).x