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"You often hear people talk about the oldest continuous culture in the world being Aboriginal culture," says geologist Professor Brad Pillans of the Australian National University."Many archaeologists have thought rock art has been a part of Aboriginal culture since earliest times...
A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
"These were dated using radiocarbon dating of charcoal buried at the same depth of engravings," he says.
Beyond engravings, the oldest reliably-dated rock art in Australia is 28,000 years old.
"The people who drew that animal could only have seen it more than 40,000 years ago," says Pillans.
David emphasises it is still uncertain whether the bird is actually a Genyornis and points instead to ochre crayons that date to around 50,000 years ago.
Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.
Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.
There is no dateable carbon from plants, charcoal or dust caught in the ochre pigment, says David.
And it's difficult to use a similar approach to that used on the limestone art so new methods need to be developed.