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It is formed by the impact of meteorites on the body’s surface. The force of the collision melts some of the impacted regolith to form objects.
The eaths radius is the correct answer, if you need proof look at nasa's website
This is due to earths location in the solar system. Earth is in the habitat zone or the Goldie locks zone, in this zone it's not too hot or not too cold for water to exist. Other planets in different star systems have liquid oceans due to them being in the habitat zone.
