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mass extinction
(Encyclopedia)mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events. The five greatest were thos...solar system
(Encyclopedia) CE5 Solar system CE5 solar system, the sun and the surrounding planets, natural satellites, dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is by far the ...atmosphere
(Encyclopedia) CE5 Atmosphere atmosphere [Gr.,=sphere of air], the mixture of gases surrounding a celestial body with sufficient gravity to maintain it. Although some details about the atmospheres of other plane...satellite, artificial
(Encyclopedia) CE5 A. Nimbus weather satellite B. Syncom communications satellite satellite, artificial, object constructed by humans and placed in orbit around the earth or other celestial body (see also space ...Arizona
(Encyclopedia) CE5 Arizona ârˌəzōˈnə [key], state in the SW United States. It is bordered by Utah (N), New Mexico (E), Mexico (S), and, largely across the Colorado River, Nevada and California (W); it touch...ocean
(Encyclopedia)ocean, interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other i...Browse by Subject
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