What would you put on your list of the great scientific revolutions of the twentieth century? Genetics? General relativity?Something to do with quantum mechanics,perhaps? One discovery that must be on that list is the theory of plate tectonics-the principle of how the rigid outer shell of our Earth (its lithosphere) moves and recycles.It provides a unifying context for the previously disparate disciplines of Earth science and was rapidly accepted across the geological community in the late 1960s.Since then,plate tectonics has arguably become a standard model in Earth science.This theoryhas experienced further developments over the last 50 years since its advent in 1967-68.