Atmosphere the mass of air surrounding the Earth; Air is all around us. It can't be seen but it is everywhere
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Troposphere-the lowest atmospheric layer; from 4 to 11 miles high Stratosphere-The region of the atmosphere above the troposphere and below the mesosphere Mesosphere- the atmospheric layer between the stratosphere and the thermosphere Thermosphere-The outermost shell of the atmosphere, between the mesosphere and outer space, where temperatures increase steadily with altitude.