8. Life has changed Earth’s atmosphere, and changes in the atmosphere

affect conditions for life. As a basis for understanding this concept:

a. Students know the thermal structure and chemical composition of the

atmosphere.

b. Students know how the composition of Earth’s atmosphere has evolved over

geologic time and know the effect of outgassing, the variations of carbon

dioxide concentration, and the origin of atmospheric oxygen.

c. Students know the location of the ozone layer in the upper atmosphere, its

role in absorbing ultraviolet radiation, and the way in which this layer varies

both naturally and in response to human activities.