Earth, Third planet in distance outward from the Sun. Believed to be about 4.56 billion years old, it is some 149,600,000 km (92,960,000 mi) from the Sun. It makes one revolution, or one complete orbit of the Sun, in about 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 40,076 km (24,902 mi). Its total surface area is roughly 509,600,000 sq km (197,000,000 sq mi), of which about 71% is water. Earth’s atmosphere consists of a mixture of gases, chiefly nitrogen and oxygen. Its only natural satellite, the Moon, orbits the planet at a distance of about 384,400 km (238,900 mi). 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; lithosphere). 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 is divided into a number of large and small plates that float on and travel independently of the mantle. Plate motions are responsible for continental drift and seafloor spreading and for most volcanic and seismic activity on Earth.
Earth Article
Earth summary
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solar system Summary
Solar system, assemblage consisting of the Sun—an average star in the Milky Way Galaxy—and those bodies orbiting around it: 8 (formerly 9) planets with more than 210 known planetary satellites (moons); many asteroids, some with their own satellites; comets and other icy bodies; and vast reaches of
Moon Summary
Moon, Earth’s sole natural satellite and nearest large celestial body. Known since prehistoric times, it is the brightest object in the sky after the Sun. It is designated by the symbol ☽. Its name in English, like that of Earth, is of Germanic and Old English derivation. The Moon’s desolate beauty
planet Summary
Planet, (from Greek planētes, “wanderers”), broadly, any relatively large natural body that revolves in an orbit around the Sun or around some other star and that is not radiating energy from internal nuclear fusion reactions. In addition to the above description, some scientists impose additional
Antarctica Summary
Antarctica, the world’s southernmost and fifth largest continent. Its landmass is almost wholly covered by a vast ice sheet. Often described as a continent of superlatives, Antarctica is not only the world’s southernmost continent. It is also the world’s highest, driest, windiest, coldest, and