abyssal

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abyssal Term to describe oceanic features occurring at great depths, usually more than c.3000m (10,000ft) below sea level. Abyssal plains cover c.30% of the Atlantic and nearly 75% of the Pacific ocean floors. They are covered by deposits of biogenic oozes formed by the remains of microscopic plankton and nonbiogenic sediments. The gradient is less than 1:1000, except for the occasional low hill. The abyssal zone is the deepest area of the ocean. It receives no sunlight, so there are no seasons and no plants, but there are many forms of life, such as sponges, crinoids (sea lilies) and brachiopods (lampshells).

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