Wandering Poles or Drifting Continents? - Four Revolutions in the Earth Sciences - page 101

Blackett departed Manchester for Imperial College in 1953, accompanied by
Clegg. They made an extensive study of the Deccan Traps from India, the same
rocks that Irving had analyzed, and duplicated his results almost exactly. 6 That
two separate laboratories, using different instruments and rock samples, got nearly
identical results was an important validation of the accuracy of the paleomagnetic
methods. Because the pole position of rocks from India did not agree with the pole
position of rocks from Britain and America, “India must have moved relative to
Northern Europe and North America,” they wrote. 7 Now the paleomagnetists had
established that rocks from three different continents each pointed to the pole in
a different place at the same time. But since all the evidence indicated that the
Earth's field had always been dipolar, the only explanation left was continental
drift.
The British paleomagnetists agreed with that statement, with one surprising ex-
ception: Stanley Runcorn. He had begun by endorsing “true polar wandering”: ac-
tual slippage of the crust as a whole relative to the rotational pole. In June 1955,
Runcorn submitted a short note to Nature based on his study of the paleomagnet-
ism of rocks from the Grand Canyon. He wrote that “these results appear to dis-
pose of the possibility that since pre-Cambrian times the continents of America
have drifted any appreciable distance from the continents of Europe and Africa.” 8
A year later, Runcorn had changed his mind and converted to mobilism. 9 As he
told Frankel, at one “moment” in conversation with another paleomagnetist, Run-
corn “became convinced that the paleomagnetic data had to be explained in terms
of continental drift.” 10 Frankel notes that even after he had interviewed Runcorn,
“it is difficult to determine precisely what motivated him to change his mind.” 11
Runcorn recalled that he and Ted Irving had “independently noticed the difference
among poles from different continents.” The differences were real “and could not
simply be explained away. That was the time of my conversion [to] continental
drift” (165-166).
How was Runcorn able to convert so painlessly? He had been working on pa-
leomagnetism for only a few years and had no lengthy record of publication and
pronouncements to renounce. Runcorn had espoused true polar wandering, but he
may have been right to do so then, before the results showing the different pole po-
sitions from different continents had come in. At that time, paleomagnetists were
uncertain whether they were seeing evidence for drift, for true polar wandering, or
for both. Runcorn was a physicist in Britain surrounded by other physicists, all led
by Blackett, who was amenable to drift. To convert, instead of having to reverse
years of expostulating against drift and run the risk of being branded a heretic by