Dating rock art
It is difficult to accurately assess the age of rock art. The thermoluminescence dating technique has been used in Kakadu to date the sand surrounding pieces of ground ochre to 50 000 years ago. Used pieces of ochre provide good evidence that there was artistic expression of some sort at this early date, although not necessarily rock art. Carbon-dating techniques require the presence of carbon-bearing organic materials, which are generally not used in the mineral paints of the Kakadu region. Carbon dating has, however, been used to date bees-wax paintings, the oldest of which was found to be about 4000 years old.
By studying the subjects and art styles and then comparing them with climatic, geological and archaeological evidence, researchers have been able to estimate the age of a number of paintings. Paintings of animals now extinct on the Australian mainland can be assumed to have been done before, or shortly after, these animals disappeared: the long-beaked echidna is thought to have become extinct 15 000 years ago; the thylacine and Tasmanian devil became extinct more recently, probably about 2000 to 3000 years ago. Paintings of other animals are linked to specific environmental conditions: estuarine conditions are thought to have begun about 6000 years ago, so paintings of estuarine fish are probably less than 6000 years old; the freshwater floodplains developed more recently, so paintings of freshwater birds such as magpie geese are probably less than 1500 years old.