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From Wikipedia, the free encyclopedia
Earth (IPA: /ɝθ/) is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. Home to the human species, it is also referred to as "the Earth", "Planet Earth", "Gaia", "Terra", "the World", and "the Blue Planet".
The Earth is the first planet known to have liquid water on the surface and is the only place in the universe known to harbor life. Earth has a magnetic field that, together with a primarily nitrogen-oxygen atmosphere, protects the surface from radiation that is harmful to life. The atmosphere also serves as a shield that causes smaller meteors to burn up before they strike the surface.
The Earth formed around 4.57 billion years ago and its only known natural satellite, the Moon, began orbiting it around 4.53 billion years ago. At present, the Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis (which is equal to 365.26 solar days). The Earth's axis of rotation is tilted 23.5° (away from the perpendicular to its orbital plane), producing seasonal variations on the planet's surface.
