ABSTRACT
Ocean sediments comprise the following: the remains of organisms that live on and in the deep-sea bottom; biological and mineral materials that are contributed by bottom currents; biological and mineral materials that sink from the ocean's surface waters, including those materials that reach those surface waters by atmospheric transport; and the products of chemical changes that take place in the sediment after deposition. Although erosion and redeposition do take place on the deep-sea floor, in many places deposition has continued without significant interruption for many hundreds of thousands, up to many millions, of years. The different components of the sediment provide evidence of past conditions, both at the ocean surface and at the ocean floor, so that past variations in temperatures, salinities, currents, chemical conditions and aeolian inputs can be inferred for very long periods of time, and over most of the oceans. Realization that such a storehouse of information on past conditions on earth existed in the oceans developed only very slowly between the Challenger and Swedish Deep-Sea Expeditions but has expanded exponentially during the past half century
