a) Divergent plate boundaries and seafloor-spreading

Due to geological and geophysical oceanography in the last decades, new techniques such as echo-sounding, rock dredging, piston coring were developed and applied to studying the oceans. These data, along with gravity and magnetics were collected all over the oceans resulting to the establishment of the existence of a worldwide mid-ocean ridge system. Furthermore it was recognized that these ridges were tensional structures and magnetic stripes have been found on the seafloor (see paleomagnetism).