Ancient camps full of data
■ Radio carbon data from prehistoric occupation sites are providing insights into Australia’s fluctuating human population levels tens of thousands of years ago.
Australian National University archaeologist Alan Williams used radio carbon-dating technology to examine charcoal dates from more than 1000 prehistoric campfires and based on this he says populations appear to have increased steadily until 25,000 years ago.
He did this by examining the isotope Carbon 14, which is absorbed by all living things from the atmosphere.
Their remains then lose the isotope at a steady rate after they die, and Carbon 14 levels provide reliable dates for any organic matter up to about 35,000 years old.
Dr Williams compared these dates with climatic change profiles provided by a recent synthesis of Australia’s palaeoclimate from the Australasian Integration of Ice core, Marine and Terrestial records project.
Co-author UWA archaeologist Winthrop Professor Peter Veth says Dr Williams’ comparison showed a clear correlation between datasets.
“Demographic models suggest populations may have been quite high before the last ice age,” he said.
After this initial increase, he said, population levels remained steady or even declined from 25,000 years ago, during the more arid Last Glacial Maximum (25,000 to 13,000 years ago) when temperatures were about ten degrees cooler.
This included archaeological “silences” — or lack of occupation data — within Australia’s arid zone during the Last Glacial Maximum.
“There are really only smaller bioregions in the arid zone where their occupation ceases to be registered,” Winthrop Professor Veth said.
“Then with the restructure in population and possibly lower carrying capacity for large portions of the continent that became more arid, population levels of demography may have actually become more negative.”
Campfire numbers began to grow again 13,000 years ago when the northern wet season reemerged.
In the west Pilbara’s Chichester Range, for example, radiocarbon dating shows people started to use rock shelters that had been unoccupied since the late Pleistocene (up to 11,700 years ago).
Winthrop Professor Veth said while population levels, occupation patterns and overall climate trends correlated strongly from 35,000 until about 5000 years ago, things then became less predictable.
He said Aboriginal people started to embrace technologies and practices that appear to have made their behaviour less dependent on easily available resources.
For example, they remained more sedentary by wet-milling grass and acacia seeds to prepare damper and seed cakes.
Archaeologist Alan Williams used radio carbon-dating technology to examine charcoal dates from 1000 prehistoric campfires.