1. From the Earth's surface extending up to between 7 and 14 kilometers is the TROPOSPHERE. This layer of the atmosphere is the densest - about 80% of the total mass of the atmosphere lies here. The troposphere is responsible for the weather on Earth.

2. The STRATOSPHERE starts where the troposphere ends, and extends to 50 kilometers up. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer. The stratosphere is very dry; the air contains little water vapor.

3. Above the stratosphere is the MESOSPHERE which extends from 50 km to about 80 km up. Temperature decreases with height throughout the mesosphere. The coldest temperatures in Earth's atmosphere, about -90° C is found near the top of this layer.

4. The next layer is the THERMOSPHERE which extends right up to 600 kilometers. Auroras occur in this layer. Temperatures rise sharply in the lower thermosphere - below 200 to 300 km altitude - then level off and hold fairly steady with increasing altitude above that height.

5. The upper limit of our atmosphere is the EXOSPHERE. It extends from the top of the thermosphere and fades away into space.

6. The IONOSPHERE is a layer of electrons and ionized atoms and molecules that stretches from about 50 kilometers above the surface of the Earth up to the edge of space at about 1,000 km, overlapping into the mesosphere and thermosphere.