Tectonic plates – Richard Jones

The notion of continental drift, after the splitting up of the super-continent Pangaea, was first put forward by Alfred Wegener (a geophysicist and meteorologist) in 1912, and was initially highly controversial. However, the theory fitted much geological sedimentary evidence, and was supported by Arthur Holmes’ studies of radiometric geochronology which postulated convective heating from the Earth’s core & mantle as being the driving force for continental drift.

Palaeomagnetic studies indicated that the continents had moved apart in longitude. Harry Hammond Hess is considered one of the “founding fathers” of the unifying theory of plate tectonics, and in 1960 he advanced the theory, now generally accepted, that the Earth’s crust moved laterally away from long, volcanically active oceanic ridges by means of sea-floor spreading. The Vine–Matthews–Morley hypothesis of 1963 showed that rocks surrounding mid-oceanic ridges exhibited symmetric patterns of magnetisation. Dan McKenzie integrated these ideas into essentially the modern theory of plate tectonics in 1967. The continents are still moving and growing, subduction of one plate under another is taking place, and mountain ranges are being formed, giving rise to seismic & volcanic activity. Richard showed an animation by Prof. Christopher Scotese of the past and predicted future movements of continental drift (e.g. see https://www.youtube.com/watch?v=uLahVJNnoZ4). Unfortunately, Richard’s talk had overrun in time, but, in view of the interest generated, it was agreed that its final 20 minutes would be deferred to a later meeting.