The title of this post comes from two lines in ‘In Memoriam A.H.H.‘ by Alfred, Lord Tennyson. The theory of plate tectonics evolved about fifty years ago so it is very unlikely that Tennyson was thinking about the hills as waves of rock flowing across the landscape. However, we now understand that Earth’s crust is divided into plates that are moving as a result of currents in the liquid magna beneath them. For example, the African plate is moving northwards crashing into the Eurasian plate causing the edges of the plate to buckle and flow forming the Alps and Pyrenees along the edge of the Eurasian plate. At the same time, the Eurasian plate is moving eastwards very slowly at a speed of about 2.5 cm per year, or about 2 metres in an average human lifetime. So, nothing stands still. Everything is a process. It’s just that some processes are quicker than others [see ‘Everything is in flux but it’s not always been recognised‘ on April 28th, 2021].