Earth is the only known planet with life on it, and its natural features are the subject of many scientific studies. It is the third planet from the Sun in the Solar System and the largest in diameter, mass and density among the planets of the terrestrial group. The main climatic features of the Earth are the presence of two large polar regions, two relatively narrow temperate zones and one wide equatorial-tropical region.[1] The amount of precipitation on the planet varies widely depending on the location and ranges from a millimeter to several meters of precipitation per year. About 71% of the Earth's surface is occupied by the ocean. The other part consists of continents and islands, and a large one part of the land inhabited by humans is in the Northern Hemisphere.