Volume including the lower part of the Lowermost region of a planetary atmosphere where convection keeps the gas mixed and maintains a steady decrease of temperature with height. Most clouds are in the troposphere. (as high as living organisms can fly or be lofted) and the surface of the earth (including the oceans and uppermost Outermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the), encompassing all the living matter of the earth.