Chapter 2

An ocean story

“Essentially the whole of plate tectonics was discovered by the palaeomagnetics people.”


The evidence for plate tectonics came from the oceans: scale also mattered. McKenzie and ParkerParkerBob Parker (1942-present) joined Madingley Rise as a PhD student in 1963, alongside McKenzie; they shared an office and had the same supervisor, Teddy Bullard. Parker was working on the propagation of the electromagnetic field from the ionosphere into the Earth, which demanded an understanding of the oceans. Parker went to IGPP Scripps for post-doctoral research and there he and McKenzie worked out the paving stone model of rigid plates rotating on a sphere about axes. Parker had produced a flexible computer programme to draw maps and he helped McKenzie incorporate earthquake first motions around the edges of the plates as instantaneous velocity vectors, a crucial step in the arguments of McKenzie and Parker 1967. considered the north Pacific Ocean basin as a whole; geological work at the time, in contrast, tended to be regional, even local. Any evidence for plate tectonics on the continents was not apparent at these scales – although the work of palaeomagnetists on land in the 1950s and 60s contains evidence that the continents had moved. “Essentially the whole of plate tectonics was discovered by the palaeomagnetics people,” says McKenzie. “It’s really interesting as to why that was not taken seriously by almost everybody in the community. …One difficulty for many people is that there was and still is no good theory as to why the dipole component of the Earth’s magnetic field should line up along the rotational axis.”

Page from Ted Irving’s field notebook recording a detailed bed-by-bed collection of red siltstones and sandstones from Inveralligin, Loch Torridon, October 1951, for palaeomagnetic processing at Jodrell Bank Radio Astronomy Station on a Blackett magnetometer.