The geology of the ocean basins has been investigated by geophysical methods and by sampling deepsea sediments. The theory of seafloor spreading, the geothermal evolution of ocean lithosphere, the subsidence history of the ocean floor, the hot-spot theory, and the theories on the development of active and passive ocean margins formulated on the basis of geophysical considerations, have been confirmed by drilling investigations. Studies of samples from beneath the deepsea floor provided evidence for climatic cooling during the Cenozoic, and yielded data for the recognition of crisis in ocean environments and for the reconstruction of paleo-oceanographic circulations.