the lowest densest part of the earth's atmosphere in which most weather changes occur and temperature generally decreases rapidly with altitude and which extends from the earth's surface to the bottom of the stratosphere at about 7 miles (11 kilometers) high. 
The troposphere is the lowest major atmospheric layer, extending from the Earth's surface up to the bottom of the stratosphere. The troposphere is where all of Earth's weather occurs. It contains approximately 80% of the total mass of the atmosphere.
