Friday, 23 February  2001

Nanjing man

Another Australian study - this time of Chinese fossils - has weighed into the controversy over the origins of modern humans, supporting the theory they evolved in many different regions of the world.

Dr Jian-xin Zhao and Professor Ken Collerson from the University of Queensland (UQ) have dated ancient human fossils in China as being at least 620,000 years old - much older than previously thought.

The researchers from the Earth Sciences Department say the findings support the theory that Asian populations evolved directly from Asian Homo Erectus, rather than evolving from populations out of Africa.

A major argument against this regional continuity theory, Dr Zhao told ABC Science Online, is that the age of Homo Erectus fossils found in Asia did not allow enough time for Homo Sapiens to evolve.

"This new date gives plenty of time for Home Erectus to evolve into Homo Sapiens," he says.

The researchers measured the decay of uranium into thorium in samples of calcite flowstone directly above recently discovered Homo Erectus fossils called Nanjing Man, in the Tangshan Cave 250 kilometres northwest of Shanghai.

In the past this method has been used to date teeth and bones, however the researchers say applying it to calcite flowstone samples has provided much more accurate dates and challenged the reliability of using fossil teeth for the purposes of dating.

"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 says. "In contrast, the University of Queensland 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.

Information provided by: http://www.abc.net.au