1. Characteristics of the

2.  A mixture of gases that surrounds the Earth.  Always changing  Protects us from the sun’s damaging rays

3.  78% Nitrogen  21% Oxygen  1% Other Gases

4.  Air pressure is the measure of the force with which air molecules push on a surface.  As altitude increases, air pressure decreases.  Atmospheric composition affects air temperature.  Air pressure increases closer to the Earth’s surface…pyramid ex.

5.  Troposphere: “turning” or “change” (gases turn and mix in this layer)  Stratosphere: “layer” (gases are layered here and do not move much)  Mesosphere: “middle” (middle layer)  Thermosphere: “heat” (temps are the highest in this layer)

6.  Troposphere -the layer in which we live -the lowest the level -the densest atmospheric layer -almost 90% of Earth’s total mass -due to changes in the temperatures & density the gases continuously mix in this layer

7.  Stratosphere -home of the ozone layer -air is very thin -contains little moisture -contains the ozone layer which protects life on Earth by absorbing harmful ultraviolet radiation -temps can get to -60 degrees C

8.  Mesosphere -middle layer -coldest layer -temp decreases as altitude increases -temps can get to -93 degrees C

9.  Thermosphere -the uppermost layer -temps increase with altitude -temps can get 1,000 degrees C -it doesn’t feel that hot

10.  You are lying in a park. Your eyes are closed, and you feel the warmth of the sun on your face. You may have done this before, but have you ever stopped to think that it takes a little more than eight minutes for the energy that warms your face to travel from a star that is 149,000,000 km away?

11.  Radiation: the transfer of energy as electromagnetic waves.  Thermal Conduction: the transfer of thermal energy through a material.  Convection: the transfer of thermal energy by the circulation or movement of a liquid or gas.  Convection Currents: A cycle of warm air rising and cool air sinking causes a circular movement of air.

12.  Q: How do differences in air density cause convection currents?  A: Cold air is more dense than warm air, so cold air sinks and warm air rises. This produces convection currents.