Earthquake, any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks. Earthquakes occur most often along geologic faults, narrow zones where rock masses move in relation to one another.
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Rivers running westwardacquiredtremendous erosive power. Following fracture lines marking weaknesses in the Earth’s crust, they dug out gorges and canyons that knifed deep into the jagged coast. To the east the land sloped more gently, and broader valleys were formed. During repeated periods of ...
bounded to the northeast by a series ofoceanic troughsand to the northwest by troughs, a chain ofcoral reefs, and a series of submarine ridges. The third major unit of the Earth’s crust in Indonesia is an extension of the belt of mountains that formsJapanand thePhilippines; the mountain...
and the beginning of theCambrian Period(541 million to 485 million years ago); their source area was probably the continental forelands ofAustraliaand Antarctica, then part of a nearby single supercontinent.Continental drift(the movement of large plates of Earth’s crust) created a distinctisland ...
Earth's principal tectonic platesThe principal tectonic plates that make up Earth's lithosphere. Also located are several dozen hotspots where plumes of hot mantle material are upwelling beneath the plates. The Atlantic is still opening along the Mid-Atlantic Ridge under the ocean, withIcelandconstit...
it is one of the oldest and most stable parts of the Earth’s crust. Its surface formations and soils were altered by the receding glaciers of thePleistocene Epoch(about 2,600,000 to 11,700 years ago). Lakes dot the fairly flat landscape, and thousands of islands form archipelagoes along...
spacecraft pictures revealed that the feature’s pinkish cloud layer can be overlain from time to time by high-altitude white clouds, producing the gray impression seen from Earth. In the late 19th century the length of the spot was about 48,000 km (30,000 miles), and since then the sp...
000 in the third decade of the 21st century. The explosive growth was a spin-off of a survey designed to find 90 percent of asteroids with diameters greater than one kilometre that can crossEarth’sorbit and thus have the potential to collide with the planet (see belowNear-Earth asteroids)...
Moon, Earth’s sole natural satellite and nearest celestial body. Known since prehistoric times, it is the brightest object in the sky after the Sun. Its name in English, like that of Earth, is of Germanic and Old English derivation.