The Troposphere

> is where all weather takes place
> is the region of rising and falling packets of air
> air pressure at the top of the troposphere is only 10% of that at sea level (0.1 atmospheres) > the thin buffer zone between the troposphere and the next layer called the tropopause

The Stratosphere and Ozone Layer

> the stratosphere, where air flow is mostly horizontal
 > the thin ozone layer in the upper stratosphere has a high concentration of ozone
> responsible for absorbing the ultraviolet radiation from the Sun
> the ozone layer was formed once O2 appeared
> UV is harmful to the evolution of life


The Mesosphere and Ionosphere

the ionosphere (or thermosphere) is where many atoms are ionized (have gained or lost electrons so they have a net electrical charge)
> the ionosphere is very thin, and it is where Aurora Borealis take place
> the most energetic photons from the Sun are absorbed here
> reflects radio waves, thereby making long-distance short wave radio communication possible