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© 2006 Encyclopaedia Britannica, Inc.
Early American furniture ► Earth-crossing asteroid I 587
outer ear middle ear inner ear
canal membrane)
Structures of the human ear. The cartilaginous auricle and the auditory canal of the outer ear direct sound waves to the middle ear. The eardrum, stretched across the end of the canal, vibrates as sound waves reach it. Vibrations are transmitted via three small bones (hammer, anvil, stirrup) to the membranous oval window, which links the middle ear to the inner ear. The cochlea is a coiled, fluid-filled tube lined with sensory hairs. Vibrations in the oval window cause movement of the cochlear fluid, stimulating the hairs to initiate impulses that travel along a branch of the audi¬ tory nerve to the brain. The eustachian tube, running from the middle ear to the nasopharynx, equalizes pressure between the middle and outer ear. The fluid-filled semicircular canals play a role in balance, as hairs in the canals respond to movement-induced changes in the fluid by initiating impulses that travel to the brain.
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Early American furniture Furniture made in the second half of the 17th century by American colonists. The earliest pieces were massive and based on English Jacobean styles. Decoration consisted of carved flower motifs or lunettes and carved scrolls and leaves, sometimes highlighted by painting; oak and pine were the most common woods. Produced in the Connecticut River valley and Massachusetts coastal settlements, it con¬ sisted mainly of chests, cupboards, tables, stools, chairs, and beds.
Early Netherlandish art Architecture, painting, sculpture, and other visual arts produced in Flanders in the late 14th and 15th century under the rule of the dukes of Burgundy. In 1384 Philip II the Bold acquired the countship of Flanders by marriage, and the Flemish-Burgundian political alliance remained intact until 1482. Philip embellished the churches and monasteries of his capital, Dijon, with sculpture, especially that of Claus Sluter, and paintings. His grandson, Phiup III the Good, patronized the arts on a grander scale, hiring Jan van Eyck and Rogier van der Weyden. Among the masters active until the end of the alliance were Robert Campin, Petrus Christus, Dirck Bouts, Hugo van der Goes, and Hans Memling.
Earnhardt, (Ralph) Dale (b. April 29, 1951, Kannapolis, N.C., U.S.—d. Feb. 18, 2001, Daytona, Fla.) U.S. automobile racer. He earned Rookie of the Year honours on the National Association for Stock Car Auto Racing’s Winston Cup series in 1979. In his career he drove to seven Winston Cup titles (1980, 1986-87, 1990-91, 1993-94), equaling the mark of Richard Petty. Earnhardt gained a reputation as an aggressive driver and became known as “the Intimidator.” He died from injuries suf¬ fered in a crash during the final lap of the 2001 Daytona 500.
Earp \'orp\, Wyatt (Berry Stapp) (b. March 19, 1848, Monmouth, Ill., U.S.—d. Jan. 13, 1929, Los Angeles, Calif.) U.S. frontiersman. He worked in the 1870s as a police officer in Wichita and Dodge City, Kan., where he befriended the gunmen Doc Holliday and Bat Masterson. He later worked as a guard for Wells, Fargo & Company. By 1881 he had moved to Tombstone, Ariz., living as a gambler and a saloon guard. His brother Virgil became town marshal, and his other brothers (James, Morgan, and Warren) bought real estate and businesses. A feud with the Clanton gang ended in a shootout at the O.K. Corral in which three of the Clanton gang were killed. In 1882 Morgan was murdered, and in retaliation Wyatt, Warren, and some friends killed two men they suspected of the crime. Accused of murder, Wyatt fled to Colorado and later settled in Califor¬ nia. Stuart Lake’s Wyatt Earp, Frontier Marshal (1931), written with Earp’s collaboration, portrayed him as a fearless lawman.
Earth Third planet in distance outward from the Sun. Believed to be about 4.6 billion years old, it is some 92,960,000 mi (149,600,000 km) from the Sun. It orbits the Sun at a speed of 18.5 mi (29.8 km) per second, mak¬ ing one complete revolution in 365.25 days. As it revolves, it rotates on its axis once every 23 hours 56 minutes 4 seconds. The fifth largest planet of the solar system, it has an equatorial circumference of 24,902 mi (40,076 km). Its total surface area is roughly 197,000,000 sq mi (509,600,000 sq km), of which about 29% is land. Earth’s atmosphere consists of a mix¬ ture of gases, chiefly nitrogen and oxygen. Its only natural satellite, the Moon, orbits the planet at a distance of about 238,860 mi (384,400 km). Earth’s surface is traditionally subdivided into seven continental masses: Africa, Antarctica, Asia, Australia, Europe, North America, and South America. These continents are surrounded by four major bodies of water: the Arctic, Atlantic, Indian, and Pacific oceans. Broadly speaking. Earth’s interior consists of two regions: a core composed largely of molten, iron- rich metallic alloy; and a rocky shell of silicate minerals comprising both the mantle and crust (see also Moho; uthosphere). Fluid motions in the electrically conductive outer core generate a magnetic field around Earth that is responsible for the Van Allen radiation belts. According to the theory of plate tectonics, the crust and upper mantle are divided into a number of large and small plates that float on and travel independently of the lower mantle. Plate motions are responsible for continental drift and seafloor spreading and for most volcanic and seismic activity on Earth.
ocean asthenosphere
Earth's interior may be identified in two distinct ways. In chemical terms, it has three basic layers (left): the crust consists of granitic and basaltic rock, the mantle of silicate materials, and the core primarily of nickel and iron. Measured by physical properties, it has five principal layers (right): the lithosphere is a rigid outer layer, the asthenosphere is a thin layer of plastically deforming material that flows under stress, the mesosphere is a rigid layer that extends down to the core, the outer core is a viscous liquid in which Earth's magnetic field is believed to originate, and the inner core is solid. The layers are not drawn to scale.
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Earth-crossing asteroid Asteroid whose path around the Sun crosses Earth’s orbit. Three groups of such asteroids—Aten, Apollo, and Amor asteroids—are distinguished by the size of their orbits and how closely they approach the Sun. The Atens and Apollos cross Earth’s orbit on an almost continuous basis, whereas only about half the Amors are Earth crossers and then only part of the time. Astronomers have mounted searches for objects that closely approach Earth, partly to determine whether they may collide with the planet, since early detection might make it possible to avert a catastrophe. According to some estimates.
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588 i Earth impact hazard ► East
1,000 Earth-crossing asteroids larger than 0.6 mi (1 km) may exist. Impacts of 0.6-mi-size asteroids are believed to occur a few times every million years. Such a collision would deliver the explosive force of sev¬ eral hydrogen bombs, possibly resulting in global climate disturbances or huge tidal waves. The impact of an object about 6 mi (10 km) in diam¬ eter is thought to have caused a massive extinction of species, including the dinosaurs, at the end of the Cretaceous Period.
Earth impact hazard The danger of collision with asteroids and com¬ ets whose orbits carry them near Earth. Space around Earth contains vast numbers of objects in a range of sizes, but only the largest, which strike very rarely on average, are thought to pose a great danger. Scientists believe such an impact caused the mass extinction of dinosaurs and other species at the end of the Cretaceous Period 65 million years ago. In addi¬ tion to creating tremendous immediate destruction, a large impact could throw great clouds of debris into the atmosphere, cutting off sunlight and causing a prolonged temperature drop—an “impact winter” (similar to a nuclear winter) that would kill plant life and bring on worldwide famine. The amount of damage depends primarily on the colliding object’s mass and relative velocity. The energy released, expressed in millions of tons (megatons) of TNT, falls between about 10 megatons and 1 billion mega¬ tons, corresponding to objects roughly 160 ft (50 m) to 12 mi (20 km) across. The last destructive impact known, the Tunguska event, occurred over Siberia in 1908. Since the 1990s, search programs have scanned for objects on possible collision courses. Should a collision appear likely, nonexplosive projectiles or, in extreme cases, nuclear weapons might suc¬ ceed in redirecting the object away from Earth.