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sea level

(Encyclopedia)sea level, the level of the sea, which serves as the datum used for measurement of land elevations and ocean depths. Theoretically, one would expect sea level to be a fixed and permanent horizontal su...

sand

(Encyclopedia)sand, rock material occurring in the form of loose, rounded or angular grains, varying in size from .06 mm to 2 mm in diameter, the particles being smaller than those of gravel and larger than those o...

Quetzalcoatl

(Encyclopedia)Quetzalcoatl kĕtˌsälkôätˈəl [key] [Nahuatl,=feathered serpent], ancient deity and legendary ruler of the Toltec in Mexico. The name is also that of a Toltec ruler, who is credited with the disc...

rhyme

(Encyclopedia)rhyme or rime, the most prominent of the literary artifices used in versification. Although it was used in ancient East Asian poetry, rhyme was practically unknown to the ancient Greeks and Romans. Wi...

Ordovician period

(Encyclopedia)Ordovician period ôrdəvĭshˈən [key] [from the Ordovices, ancient tribe of N Wales], second period of the Paleozoic era of geologic time (see Geologic Timescale, tablegeologic timescale, table) fr...

space probe

(Encyclopedia)space probe, space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is...

Rocky Mountains

(Encyclopedia)Rocky Mountains, major mountain system of W North America and easternmost belt of the North American cordillera, extending more than 3,000 mi (4,800 km) from central N.Mex. to NW Alaska; Mt. Elbert (1...

observatory, orbiting

(Encyclopedia)observatory, orbiting, research satellite designed to study solar radiation, electromagnetic radiation from distant stars, the earth's atmosphere, or the like. Because the atmosphere and other aspects...

Dylan, Bob

(Encyclopedia)Dylan, Bob dĭlˈən [key], 1941–, American singer and composer, b. Duluth, Minn., as Robert Zimmerman. Dylan learned guitar at the age of 10 and autoharp and harmonica at 15. After a rebellious you...

Great Plains

(Encyclopedia)Great Plains, extensive grassland region on the continental slope of central North America. They extend from the Canadian provinces of Alberta, Saskatchewan, and Manitoba south through W central Unite...