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Il y a 3 jours · Rare-earth elements occur in nature in combination with phosphate ( monazite ), carbonate - fluoride ( bastnäsite ), and oxygen anions. In their oxides, most rare-earth elements only have a valence of 3 and form sesquioxides (cerium forms CeO2 ). Five different crystal structures are known, depending on the element and the temperature.
Il y a 5 jours · Earth - Differentiation, Formation, Structure: Once hot, Earth’s interior could begin its chemical evolution. For example, outgassing of a fraction of volatile substances that had been trapped in small amounts within the accreting planet probably formed the earliest atmosphere. Outgassing of water to Earth’s surface began before 4.3 billion years ago, a time based on analysis of ancient ...
Il y a 5 jours · Students grades 5-8 can dig deeper into STEM topics and experience the thrill of exploration and discovery.
Il y a 5 jours · Earth - Planet, Atmosphere, Geology: The mean distance of Earth from the Sun is about 149,600,000 km (92,960,000 miles). The planet orbits the Sun in a path that is presently more nearly a circle (less eccentric) than are the orbits of all but two of the other planets, Venus and Neptune. Earth makes one revolution, or one complete orbit of the Sun, in about 365.25 days. The direction of ...
Il y a 3 jours · Battlefield Earth (taglined as Take Back the Planet and subtitled on-screen as A Saga of the Year 3000) is a 2000 American science fiction film based on the 1982 novel of the same name by Scientology founder L. Ron Hubbard. It was directed by Roger Christian and stars John Travolta, Barry Pepper, and Forest Whitaker. The film follows a rebellion against the alien Psychlos, who have ruled Earth ...
Il y a 2 jours · The Moon is Earth 's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have over time synchronized the Moon's orbital period ( lunar month) with its rotation period ( lunar day) at 29.5 Earth days, causing the same side of the Moon ...
Il y a 3 jours · The dashboard displays the next five Earth approaches to within 4.6 million miles (7.5 million kilometers or 19.5 times the distance to the moon); an object larger than about 150 meters that can approach the Earth to within this distance is termed a potentially hazardous object. The average distance between Earth and the moon is about 239,000 ...
