ABSTRACT
Much of the technology used to explore the sea comes from military applications, weather forecasting, and the energy and mining industries, each of which has an interest in better understanding the oceans. The composition of the oceans changed gradually as granitic continents began to form and as plants changed the proportion of carbon dioxide and oxygen in the atmosphere. Oceanic crust is thinner and denser than continental crust, which is why it floats lower on the mantle. Sedimentary cover is thin to absent over the mid-ocean ridges and increases in thickness away from the ridges. Deep sea sediments consist of the small shells of plankton that slowly rain down on the seafloor, volcanic ash, and fine-grained continental sediments that extend far out into the sea as turbidity currents. The deep seafloor lies between the mid-ocean rise and the continental slope and is known as the abyssal plain.
