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The Seafloor (69) Contiental Shelf • Ocean basins, which are low areas of Earth that are filled with water, have many different features. • The continental shelf is the gradually sloping end of a continent that extends under the ocean as deep as 350 meters. • Beyond the shelf, the ocean floor drops more steeply, forming the continental slope. • The continental slope extends from the outer edge of the continental shelf down to the ocean floor. • Beyond the continental slope lie the trenches, valleys, plains, mountains, and ridges of the ocean basin. • In the deep ocean, sediment, derived mostly from land, settles constantly on the ocean floor. • These deposits fill in valleys and create flat seafloor areas called abyssal plains. • Some areas of abyssal plains have small hills and seamounts. • Seamounts are underwater, inactive volcanic peaks. Ridges and Trenches • Mid-ocean ridges can be found at the bottom of all ocean basins. They form a continuous underwater ridge approximately 70,000 km long. • A mid-ocean ridge is the area in an ocean basin where new ocean floor is formed • As crustal plates move, the ocean floor changes. • When ocean plates separate, hot magma from Earth’s interior forms new ocean crust. • New ocean floor forms along mid-ocean ridges as lava erupts through cracks in Earth’s crust. • When the lava hits the water, it cools quickly into solid rock, forming new seafloor. Subduction Zone • On the ocean floor, subduction zones are marked by deep ocean trenches. • A trench is a long, narrow, steep-sided depression where one crustal plate sinks beneath another. • http://www.youtube.com/ watch?v=wP380-Iaoos Life in the Ocean • Marine organisms such as plants and algae use energy from the Sun to build their tissues and produce their own food. • This process of making food is called photosynthesis. • Chemosynthesis involves using sulfur or nitrogen compounds as an energy source, instead of light from the Sun, to produce food. • Bacteria that perform chemosynthesis using sulfur compounds live along mid-ocean ridges near hydrothermal vents where no light is available. http://www.youtube.com/watch?v=X otF9fzo4Vo • Marine organisms that drift with the currents are called plankton. • Plankton range from microscopic algae and animals to organisms as large as jellyfish. • Most phytoplankton plankton that are producersare one-celled organisms that float in the upper layers of the ocean where light needed for photosynthesis is available. Plankton • One abundant form of phytoplankton is a once-celled organism called a diatom. • Diatoms and other phytoplankton are the source of food for zooplankton, animals that drift with ocean currents. Coral Reefs • Corals thrive in clear, warm water that receives a lot of sunlight. • Each coral animal builds a hard capsule around its body from the calcium it removes from seawater. • Each capsule is cemented to others to form a large colony called a reef. • A reef is a rigid, wave-resistant structure built by corals from skeletal material. • https://www.youtube.com/watch?v=wbNeIn3vVK M • What is the continental shelf? • The continental shelf is the gradually sloping end of a continent that extends under the ocean. • Which structure extends from the outer edge of the continental shelf to the ocean floor? – A. abyssal plain – B. continental slope – C. oceanic trench – D. seamount • What is the area in an ocean basin where new ocean floor is forming? • New seafloor forms at mid-ocean ridges as lava erupts through cracks in Earth’s crust. • Which process involves using sulfur or • nitrogen compounds as an energy source to produce food? – A. chemosynthesis – B. nitrosynthesis – C. photosynthesis – D. sulfurosynthesis