The troposphere is the lowest layer of Earth's atmosphere, which contains almost all of the weather, 99 percent of the water vapor and as much as 80 percent of the atmosphere's mass. The troposphere is 12 miles thick at the equator and four miles thick at the poles. The temperature drops from roughly 62 F at the surface to minus 60 F at the upper boundary.
The troposphere contains most of the clouds in the atmosphere. Weather happens in this layer because of dramatic changes from the warm surface to the cold upper boundary. Water vapor concentrates in the lower part of the troposphere because of warmer temperatures. Warming of this atmospheric layer occurs at the surface due to sunlight heating up the ground or ocean.
Near the tropopause, or upper boundary of the troposphere, the jet stream exists as a turbulent river of air that travels at 250 mph. This upper layer contains ice crystals instead of liquid water. Just above the tropopause is the stratosphere, where air temperatures change little and the air is much thinner. The word "troposphere" was first used in 1902 by French meteorologist Leon Philippe Teisserenc de Bort, who pioneered the use of weather balloons to collect data, according to Weather Online.