LAYERS OF THE ATMOSPHERE
The atmosphere is divided into different layers
that are defined by the temperature and how the temperature changes with
altitude. The lowermost layer is called the troposphere.
Here temperature generally decreases with height. This is because as you
go higher, you're moving farther away from the main heat source - the
Earth itself. The troposphere extends from the surface up to about 10-15
km (6-9 miles) in altitude. "Weather" occurs
in the troposphere, and this is where most of the clouds that we typically
The layer of the atmosphere just above the troposphere is the stratosphere, which extends up to about 50 km (30 miles). In this layer, which is higher than most planes fly, temperature increases with height. This is because ozone in the stratosphere absorbs sunlight, heating up the air around it. Some people call the stratosphere the "ozone layer" because most of the ozone in the atmosphere is in the stratosphere.
Above the stratosphere is the mesosphere, where temperature again decreases with height. This decrease continues up to about 90 km.
Finally, the highest layer is the thermosphere, where temperature once again increases with height. This is because molecular oxygen in the thermosphere absorbs sunlight.
The upper boundaries of the troposphere, stratosphere and mesosphere are called the tropopause, stratopause, and mesopause, respectively. The "pause" suffix indicates that this is the "top" of the layer, just like a pause in ordinary speech indicates an end to something.