Curiously, although plate tectonics is very good at describing what happens to the sea floor and the changing distribution of the continents, it is of little help in describing what happens when the continents themselves deform. They behave in a completely different way from the oceanic plates. In the oceans, plate boundaries are very narrow and localized, but on the continents they are spread out and diffuse. When continents collide they crumple up over vast areas—such as from India to Mongolia. When they stretch over wide areas they form basins that fill up with sediment and contain much of the world’s oil and gas. Moreover, the continents seem to have a memory, as they break again and again in the same place, even though the deformation episodes may be millions of years apart. Why should the continents be so different from the oceanic plates? (60 minutes)