19 February 2001

UQ researchers have dated ancient human fossils in China as being at least 620,000 years old - much older than previously thought.

Dr Jian-xin Zhao and Professor Ken Collerson from UQ's Earth Sciences Department obtained the dating by analysing rock samples directly above Homo Erectus fossils in the Tangshan Cave, 250 kilometres northwest of Shanghai.

The finding supports the 'multi-regional' evolution model that argues modern Asian populations evolved directly from Asian Homo Erectus, rather than evolving from populations out of Africa.

Dr Zhao says attempts to piece together human evolutionary history had been hampered by the fact that the ages of the fossils were well beyond the dating range of radiocarbon.

'However the recent discovery of the Tangshan Cave Homo Erectus fossils - known as Nanjing Man, an accepted equivalent of the famous Peking Man - gave us an opportunity to obtain accurate dating,' Dr Zhao said.

'Fortunately, the Nanjing Man fossils are directly below calcite flowstone. Using the state-of-the-art thermal ionisation mass spectrometer at UQ we were able to accurately date these samples by measuring the decay of uranium into minute amounts of thorium.

'Therefore we can confidently say the Nanjing Man fossils are older than 580,000 years and probably at least 620,000 years old, which is the application limit of this dating technique.'

Professor Collerson says the results also challenge the reliability of other model-dependent dating techniques widely used in the study of hominid evolution, such as electron-spin-resonance (ESR) and U-series dating of fossil teeth.

'Age estimates derived from teeth or bones depend very much on how and when uranium was taken up during fossilisation process, and are often younger than the true ages,' Professor Collerson said. 'In contrast, the UQ dates were derived from dense and pure crystalline flowstone that was closed to uranium and thorium mobility and are therefore more reliable.'

The findings, developed in collaboration with Dr Kai Hu and Dr Han-kui Xu from Nanjing, were published recently in the international journal Geology, and the significance of the research was acknowledged this week by the Editor of the prestigious Science journal.

For more information contact Dr Jian-xin Zhao (ph. 07 3365 2193), Professor Ken Collerson (ph. 07 3365 8505) or Peter McCutcheon at UQ Communications (ph. 07 3365 1088, 0413 380012, p.mccutcheon@mailbox.uq.edu.au).