Layer 3: Mesosphere
The third layer, or middle layer, of the atmosphere is called the mesosphere. This layer is between approximately 50 km and 80-85 km above the surface.
This layer contains gases including oxygen molecules but they become less abundant as the distance from Earth increases. This picture shows mesospheric clouds; it was taken by an astronaut.
An interesting aspect of the mesosphere is that the gases are thick enough to slow down meteorites. As the meteorite slows down it burns up leaving a fiery trail.
In contrast to the stratosphere, the temperatures in the mesosphere are colder at higher altitudes and warmer at lower altitudes. Temperatures decrease with height because the gases become less abundant with height and thus absorb less radiation at higher altitudes.