The word troposphere stems from the Greek "tropos" for "turning" or "mixing". This region, constantly in motion, is the densest layer. Nitrogen and oxygen are the primary gases within this region. The change of temperature with height is larger than in other layers, the temperature decreasing with altitude.
The tropopause marks the limit of the troposphere and the beginning of the stratosphere. The temperature above the tropopause increases slowly with height up to about 50 km.