The layer of Earth’s atmosphere extending from the surface upward about 10–15 kilometers, where most weather occurs, is the troposphere.
It is the atmosphere’s lowest layer and contains roughly 80% of its total mass, along with about 99% of atmospheric water vapor and aerosols. Those ingredients, combined with heating from Earth’s surface, drive convection, cloud formation, wind, rain, snow, and storms.
The troposphere does not have one fixed height. It averages about 17 kilometers above the equator and about 9 kilometers above the poles, varying with season and weather. Its upper boundary is the tropopause, above which the stratosphere begins. In the troposphere, temperature generally decreases with altitude at an average rate of about 6.5°C per kilometer.
A frequent mistake is saying that all atmospheric activity ends at the tropopause. Most weather is concentrated below it, but powerful thunderstorms can briefly overshoot into the lower stratosphere. The stratosphere is better known for its ozone layer and its temperature pattern, which differs from that of the troposphere.