McKenzie and ParkerBob 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. 1967 sets out what they called the ‘paving stone theory’, although the term did not catch on. They used Euler’s theorem to describe the geometry of rigid regions – paving stones – and their rotation about poles, and demonstrate how it works with data from around the North Pacific Ocean. They link the nature of plate boundaries to the geological phenomena that occur there – ridges, trenches, volcanoes, earthquakes – and note that mantle convection cells seem unlikely to coincide with plate boundaries. Parker’s map projection programme tracked the rotations; the orientations of the slip vectors of earthquakes were also used for the first time to show the instantaneous movements at plate boundaries. In this paper the authors routinely described the rigid regions as ‘plates’, but do not use the phrase ‘plate tectonics’.