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Atmosphere

The atmosphere is a mixture of different gases, particles and aerosols collectively known as air which envelops the Earth. The atmosphere provides various functions, not least the ability to sustain life. The atmosphere protects us by filtering out deadly cosmic rays, powerful ultraviolet (UV) radiation from the Sun, and even meteorites on collision course with Earth. Although traces of atmospheric gases have been detected well out into space, 99% of the mass of the atmosphere lies below about 25 to 30km altitude.