Expanding Earth

Andy Kelly’s letter [ FT362:75] brings to mind the old idea of the expanding Earth as an explanation for continental drift. It is such a neat idea; given that in the distant geological past, all of Earth’s land was joined together in one super-continent, one can suppose that this may at that time have covered the entire planet. Then if the Earth started to expand, the continental crust would have to break up and separate into the individual continents we see today. One of the chief exponents of this idea was Alfred Wegener. He is sometimes credited with discovering plate tectonics, but this is false. He wrote about continental drift; the correct explanation of why continents are mobile (plate tectonics) did not come for another 30 years with the work of people like Dan Mackenzie and Drum Matthews.

Which brings me to something I call the “Wegener Defence”, which you see quite often advanced by those with heterodox or pseudoscientific views, who sometimes feature in the pages of FT. This goes: “People were scornful of Wegener because he was an amateur, but he was right!” (Hence, or otherwise, I must be right also.) People were scornful of Wegener not because he was an amateur, but because he was wrong. Not about continental drift, but about the expanding Earth hypothesis.

Actually, it is not totally impossible for a planet to change size: Mercury has shrunk (see P Byrne, ‘Mercury: the incredible shrinking planet’, A&G, vol 59, 2018, pp 1419). It has a very thin crust over its mantle and core. When the inner planet cooled, it contracted, and the resulting shrinkage caused the crust to buckle and form ridges, which have been observed by missions sent to the planet (Mariner 10 and MESSENGER). Roger Musson Edinburgh