As a layer of air, the stratosphere is quite stable, especially when compared with the lowest layer, the troposphere, in which most of the atmosphere's weather occurs. Most of the movement of air in the stratosphere is horizontal, rather than rising and failing as in the troposphere.
The cruising altitude for jet airliners is often within the stratosphere's lower reaches because of the lack of turbulence. Because the air is very thin toward the top of the stratosphere, jets cannot fly any higher than that level of the atmosphere.
Toward the upper reaches of the stratosphere is the ozone layer. Ozone is a molecular form of oxygen consisting of three oxygen atoms bound together, rather than the much more common two.
The stratosphere's ozone layer absorbs more than 90 percent of the energy from ultraviolet light emitted by the sun. Such light is quite harmful to living organisms, and if there were no ozone layer, damage to plants and animals would be significant.
Because of its relative calm, the stratosphere is slow to disperse materials it receives. Volcanic eruptions periodically eject material into the stratosphere, where it stays for months or even years, sometimes cooling the surface of the Earth temporarily (this happened after the massive explosion of the Tambora volcano in Indonesia in 1815).
Various schemes for slowing down the warming of the Earth have been proposed, some involving adding man-made materials to the stratosphere. It isn't clear yet that these ideas would work, and it also has been argued that the ozone layer might be affected adversely by such steps.
