During the Ice Age, when rainfall was higher, Lake Mungo would have been a lush area to live in, teeming with wildlife. They are not 'calibrated' in the sense that engineers use the trerm whereby they confirm the measurement accuracy against something where the value is known.There is no object where its age is known beyond historical times. Whatever dating methods are measuring, it's not "age" in the customary sense.by Tas Walker Darwin considered the Australian Aborigines as primitive and not much evolved from the ‘anthropoid apes’.He anticipated that the ‘wilder races’ would become extinct because survival of the fittest meant they would be superseded by the evolutionarily-advanced ‘civilised’ races.That is why we won’t accept any date that contradicts the eyewitness evidence of human history recorded in the Bible. In short, the dates are wrong because they are based on wrong The uranium methods do not make the correct assumptions about the initial conditions of the samples or about the effects of changing environmental conditions through time. After the Flood, and after the confusion of languages at the Tower of Babel (Genesis 11), their ancestors migrated to Australia.As the populations grew, they spread out over the continent.They used different samples of bone and sand and different dating methods—electron-spin resonance (ESR), optically-stimulated luminescence (OSL), thorium-uranium (Th/U) and protactinium-uranium (Pa/U). See Dating methods.) And the results from all the different methods agreed closely. The new date meant that the history of Australian occupation would have to be rewritten and it also affected the ideas of human evolution in other parts of the world.
I do find it quite extraordinary that the materialists\naturalists\uniformitarians\actualists\evolutionists continually lecture everyone about how their conventional dates are supposedly water-tight because they're confirmed by the consilience of multiple methods...
Variation in climate since the end of the post-Flood Ice Age is complex, and depends on location and timing.
Mary White in her "After the Browing" in the chapter "Descent from the Glacial Peak ..." discusses variation in lake levels in central New South Wales as an indicator of rainfall.
You would have to look up the ANU paper to get the details.
One factor is that the different methods are calibrated to give similar results.
Yes, there has been a lot of work done measuring and documenting the isotopes in the earth's crust. As you can imagine this is an enormous task and their interpretations depend on the assumptions that are made about how the earth formed and what happened to it over its history.