The Earth's Atmospheres.

2. The original atmosphere may have been similar to the composition of the solar nebula and close to the present composition of the Gas Giant planets, like Jupiter.

4. The troposphere is where all weather takes place; it is the reg

ion of rising and falling packets of air. The air pressure at the top of the troposphe

re is only 10% of that at sea level.

5. Above the troposphere is the stratosphere, where air flow is mostly horizontal. The formation of this layer is a delicate matter,since only when oxygen is produced the atmosphere can an

 ozone layer form and prevent an intense flux of ultraviolet radiation from reaching the surface, where it is quite hazardous to the evolution of life.

6. The ozone layer is primarily responsible for absorbing he ultraviolet radiation from the Sun.

7. This picture shows the ozone layer which is the darkest blue line in the sky of this picture.

8. The structure of the ionosphere is strongly influenced by the charged particle ind from the sun, which is in turn governed by the level of Solar activity. One measure of the structure of the ionosphere is the free electron density,

 which is an indicator of the degree of ionization.