Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being a water world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth´s water is contained in its global ocean, covering 70.8% of Earth´s surface. The remaining 29.2% of Earth´s surface is land, most of which is located in the form of continental landmasses within one hemisphere, Earth´s land hemisphere. Most of Earth´s land is somewhat humid and covered by vegetation, while large sheets of ice at Earth´s polar deserts retain more water than Earth´s groundwater, lakes, rivers and atmospheric water together. Earth´s land is part of Earth´s crust, consisting of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Inside Earth´s crust is a liquid outer core that generates the magnetosphere, deflecting most of the destructive solar winds and cosmic radiation.
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