La Trobe archaeologist makes amazing find (Issue 18, 2011)
Magnetic dating of rocks by La Trobe University archaeologist Dr Andy Herries has helped confirm a date of almost two million years ago for a number of South African fossils that made world headlines last year.
Dr Herries is part of a global team which includes scientists from the University of Melbourne and James Cook University, whose work has been published in a series of five papers in the international journal Science.
The initial discovery of the fossil in cave sediments at Malapa in South Africa was featured last April as the cover story in Science. Suspected then to be at least 1.8 million years old, it generated wide-spread speculation as to whether it is the fossil link between more primitive ape-like fossil human species (Australopithecus) and fossils that are more human-like and in our own Genus (Homo).
The team since then has been engaged in a range of further high-level scientific research to verify the dating and more than five specimens have been identified, including babies, juveniles and adults.
Dr Herries dated the fossil bearing layers using palaeomagnetism and says it appears the fossils were deposited in the Malapa Cave at 1.98 million years during an extremely short reversal in the Earth’s magnetic field – a 3000 year long period when the magnetic field reversed itself by 180 degrees and back again.
Dr Herries has worked in South Africa for many years and has been involved in a number of important cave finds relating to human ancestry.
In 2007 he helped discover the oldest evidence for humans eating seafood and their use of red ochre some 164 000 years ago, and in 2009 the oldest evidence for the heat treatment of stone tools at 72 000 years ago. This work at Pinnacle Point pushed back the earliest known evidence for when humans began to think and behave like we do.
Dr Herries, one of the world’s leading specialists in cave archaeology and dating archaeological and fossil bearing sites, said that caves provide us with the potential to date and understand these short geomagnetic field events in a unique way.
He says it is not known exactly what effect such reversals in the Earth’s magnetic field would have on biological organisms, but during these shifts, the magnetic field decreases causing more cosmic radiation to reach the Earth’s surface.
‘The link between such an unusually rich fossil assemblage and such a short geomagnetic field event is intriguing but may just be pure coincidence. Only future research may answer the question over whether there is a potential link.’
Dr Herries says that the current magnetic field has been declining rapidly over the last 2000 years, and given that the last major geomagnetic field reversal took place 780,000 years ago, we are overdue for one – but probably not for at least 2000 years.
‘Our ability to date and correctly identify these short geomagnetic field events is crucial as it will enable us in the future to both better date fossil and archaeological sites as well as understand the physical workings of our own planet and its core.
‘A collaborative effort between a large group of international scientists has made these discoveries possible,’ says Dr Herries.
The study was co-ordinated by Professor Lee Berger from the University of the Witwatersrand in Johannesburg.