1. The basic idea

‘The basic idea’ presents the principles of plate tectonics and describes how this revolutionary theory took hold. It begins with Alfred Wegener in 1912, who proposed the concept of continental drift and a former huge continent, Gondwanaland. In the face of strong opposition, this theory was supported by the development of palaeomagnetism in the 1950s and, in the 1960s, became subsumed within the broader framework of plate tectonics.

Three major events precipitated this change: a switch in emphasis from continents to ocean basins and their exploration; rapid growth in seismology; and a shift in perspective from the chemical stratification of the Earth, in terms of crust and mantle, to another that emphasized strength—a strong lithosphere, some 100–200 km thick, overlying a weak asthenosphere.