The troposphere is the lowest and thickest layer of the atmosphere. In contact with Earth's surface, the troposphere is heated by solar illumination and conduction. The tropopause is the boundary layer between the troposphere and the stratosphere.

The thickness of the troposphere depends upon a number of atmospheric variables at latitude. The troposphere ranges from a thickness of approximately 5.5 mi (9 km) in the polar regions, to a thickness of approximately 10 mi (16 km) in equatorial regions.

Although the troposphere contains more than 70% of Earth's atmosphere by weight, it is much thinner than the stratosphere or ionosphere. Because density increases with increasing mass, the troposphere exhibits a high pressure and density gradient wherein density and pressure decrease with increasing altitude.

Weather phenomena (e.g., rain, snow, etc.) take place in the troposphere. Convective currents provide mixing of air masses with different temperatures. These currents pass through...