9781422277539

Words to Understand

basalt— a heavy, dark rock that forms the floors of the oceans, and some oceanic islands such as the Galápagos, Hawaii, and Iceland. continent— a slab of relatively light rock that “floats” on the heavier rock of the Earth’s mantle. The Earth has seven continents: Africa, Antarctica, Asia, Australia/Oceania, Europe, North America, and South America. current— a large-scale movement of ocean water caused by heating and cooling combined with the rotation of the Earth. mantle— the thick layer of heavy rock that lies beneath the Earth’s crust, and forms most of the volume of the Earth. mid-ocean ridge— a double chain of underwater mountains that extends along a rift in the ocean floor. New ocean floor is created at mid-ocean ridges, as the Earth’s crust on each side is pulled apart. minerals— the natural materials that make up rocks. They are carried in ocean water, and many are used as nutrients by the tiny plants of the plankton. ocean floor— the bed of the deep ocean, beyond the continental shelves. It is made of basalt covered with fine silt, or “ooze.” tide— a movement of water from one place to another caused by the gravity of the Moon, and modified by the gravity of the Sun. Makes the water level rise and fall, and causes local water flows called tidal streams. trench— a deep rift in the ocean floor, created when oceanic crust is dragged down into the mantle rock by movements within the Earth.