ANU Historic Paleomagnetic Laboratory, 1955-1964
October 2008 saw the fiftieth anniversary of the publication of a very important paper by ANU geophysicists Ted Irving and Ron Green. The paper described the polar wander path that had been obtained by measuring the palaeomagnetism of rocks of various ages and from many locations around Australia.
A polar wander path was the postulated explanation for the very different directions of the magnetism found in rocks from different locations and of different ages.
When igneous rocks solidify the iron rich minerals line up with the magnetic orientation of the Earth's field at the time. Most geologists up to the 1950s believed that the continents had always been in their present location, so when the palaeomagnetism in rocks showed different directions from the Earth's present magnetism, and knowing that the magnetic poles actually do move, geologists were prepared to accept that the poles had wandered more widely in times past.
At the time of the publication of the Irving and Green paper, a couple of polar wander paths had been determined from northern hemisphere rocks. Although these paths were not identical, it was felt that they could be reconciled. The significance of the polar wander path established by Irving and Green was that it was very different: there was no way it could be reconciled with the northern hemisphere path. The only way both could be true was for the continents to have moved relative to each other.
Subsequently another ANU geologist Ian McDougall used the magnetic hut for research on rocks from the Hawaiian Archipelago to discovery the history of reversals of the Earth's magnetic poles. The islands, formed as the Pacific plate moves north west over a hot spot, are progressively younger as you move eastward over the chain.
At the time of McDougall's work the new potassium argon dating method meant that he could age the rocks and correlate their magnetic orientation with their actual age, the most recent having what we consider the normal north-south orientation, but with a number of reversals showing up in the older rocks moving westward up the chain. This finding played an important part in developing the theory of plate tectonics.
On a cold and blustery 22nd October 2008 the ACT branches of the Geological Society of Australia and the Australian Society of Exploration Geophysicists gathered near the Forestry Building and the Research School of Biological Sciences at ANU to unveil a plaque on the remaining part of the old Magnetic Hut that had been built for Irving's research. The original hut, built in 1955 of wood with copper nails, had been the only ANU building on the Black Mountain side of Sullivan's Creek at the time. Its site is now part of the RSBS, unfortunately hidden behind a locked gate and a high metal fence. This means that the plaque is also not visible to passers by, but for anyone interested in the growth of human understanding of the Earth, the history of science and the worth of Australian science, this is an important location.
A footnote to this is Ted Irving's own story:
As a PhD student in Cambridge, Ted had studied palaeomagnetism in rocks in Scotland and India, indicating that they had moved relative to the North Pole. Prof Jaeger appointed him as a Research Fellow at the ANU on the strength of this work. While Ted was on route to Australia the news came through that the examiners had decided to fail him. Jaeger had faith in Ted's abilities and continued with the appointment. Ted's achievements thoroughly justified Jaeger's faith. As the theory of plate tectonics gained ground in scientific circles, Ted was rewarded with other degrees including a DSc from Cambridge in 1965, and fellowship of the Royal Society in 1979.
By Jenny Wanless
Questacon Explainer