The region of the atmosphere extending from the top of the troposphere (the tropopause), at heights of roughly 10–17 km, to the base of the mesosphere (the stratopause), at a height of roughly 50 km. The stratosphere is characterized by constant or increasing temperatures with increasing height and marked vertical stability. It owes its existence to heating of ozone by solar ultraviolet radiation, and its temperature varies from −85°C or less near the tropical tropopause to roughly 0°C at the stratopause. While the major constituents of the stratosphere are molecular nitrogen and oxygen, just as in the troposphere, the stratosphere contains a number of minor chemical species that result from photochemical reactions in the intense ultraviolet radiation environment. Chief among these is ozone, the presence of which shelters the underlying atmosphere and the earth's surface from exposure to potentially dangerous ultraviolet radiation. See atmospheric shell.