a) Divergent plate boundaries and seafloor-spreading

Following the Second World War, geological and geophysical oceanography applied newly developed techniques such as echo-sounding, rock dredging, and piston coring to the study of the oceans. These data, along with gravity and magnetic data were collected throughout the oceans, resulting in the discovery of a worldwide mid-ocean ridge system. Furthermore, it was recognized that these ridges were tensional, not compressional structures  that could be deciphered using magnetic stripes on the sea floor (see paleomagnetism).