Composition of the Atmosphere  The atmosphere is a mixture of gases surrounding Earth. Nitrogen (78%), the most common atmospheric gas, is released when dead plants and dead animals break down and also when volcanoes erupt. Oxygen (21%), the second most common atmospheric gas, is made by phytoplankton and plants. The remaining 1% of the atmosphere is made up of argon, carbon dioxide, water vapor and other gases.

Air Pressure (Atmospheric Pressure)  Gravity pulls gas molecules toward Earth, causing Air Pressure, which is the force with which air molecules push on a surface. Strongest at Earth’s surface Air Pressure decreases as altitude increseses

Temperature  Also changes as altitude increases  The composition of atmospheric layers affect their temperature.  The temperature differences result from the amount of gases present in each layer that absorb solar energy  As the amount of gases that absorb solar energy increases, the temperature increases

WRITING RESPONSE  Where would you encounter the lowest air pressure; on the beach or on the top of a mountain? Why?  What determines how hot or cold an atmospheric layer is?

Layers of the Atmosphere  The Earth’s atmosphere is divided into five layers based on their composition. The Silly Mouse Took Ex-lax R T E H X O R S E O P A O R S O T S M P S O P O H P S H S E H P E P R E H R H E R E E E E R R E

Troposphere  Lowest layer of the atmosphere, lying next to Earth’s surface. Temperature decreases with altitude.  Contains almost 90% of the atmosphere’s mass.  Nearly all weather occurs in this layer.  Water vapor, clouds, air pollution, and organisms are also found here.

Stratosphere  The atmospheric layer above the troposphere.  Contains little moisture  Lower stratosphere is extremely cold, but temperature increases as altitude increases in the stratosphere. The Ozone Layer- The upper layer of the Stratosphere. it absorbs UV radiation from the sun, warming the air  protects life on Earth.

Mesosphere  The middle layer of the atmosphere.  Coldest layer  Temperature decreases as altitude increases, just like the troposphere.  The upper layer of the Mesosphere (lower portion of the Thermosohere) is called the Ionosphere

Ionosphere  The lower part of the thermosphere is considered the Ionosphere.  As a result of N 2 atoms and O 2 atoms absorbing the radiation, temperature in the thermosphere rises, and gas particles become electrically charged  ions.  Ions within the ionosphere can radiate energy as shimmering lights called auroras, a.k.a. the Northern and Southern Lights.

Videos  Antarctica Auroras Antarctica Auroras  Aurora Northern Lights as seen from Space Aurora Northern Lights as seen from Space

Thermosphere  Uppermost atmospheric layer.  Temperature again increases steadily with altitude because nitrogen and oxygen atoms absorb solar radiation. This releases thermal energy.  No data to determine its upper boundary. Blends with the vacuum of space (exosphere).

Exosphere  The last layer of the atmosphere. Very difficult to determine where it stops and space begins  Very few atoms in this layer of the atmosphere