The principle, espoused by James Hutton in the 18th Century and championed by Charles Lyell in the 19th Century, that fundamental biological, chemical and physical processes on and in Earth have operated in much the same way for hundreds of millions of years. It was well summarised by Lyell as in the phrase: “the present is the key to the past”. The opposing principle is known as ‘catastrophism’ whereby intervals of stasis are punctuated by short-lived episodes of violent upheaval – catastrophes.