Twentieth-century oceanographic surveys have revolutionized our view of the planet and how it works by revealing the surface features- the topography -and nature of the ocean floor. In the early 1960s there was a plan to drill a borehole to penetrate the mantle. The "Mohole" was to be drilled where the crust was thinnest. This meant drilling in deep water from a floating ship.Seismic investigation (p. 40) had already shown that the ocean floor has a layered structure. The Mohole would sample the ocean floor and reveal the nature of the layers. Mohole never reached the Moho- the boundary where the mantle meets the crust (p. 40). Instead, in 1964, the US drilling ship Glomar Challenger began to roam the oceans, drilling into sediment and ocean floor Detailed mapping is now carried out by remote sensing apparatus towed from floating ships, and in orbiting satellites. Computers are used to visualize oceanic water circulation.