1. ATMOSPHERE THE LAYERS OF GASES THAT SURROUND THE EARTH

2. COMPOSITION: 78% Nitrogen 21% Oxygen 1% Other Gases Lower atmosphere is a mixture of many gases called air Remains the same until about 80km altitude  Above 80km air is extremely thin, almost a vacuum 99% of the atmosphere’s weight is within 32km of the surface

3. CHANGES IN THE EARTH’S ATMOSPHERE When earth was formed volcanic eruptions released gases such as CO 2  called outgassing  produced a poisonous atmosphere About 2.5 bya cells began photosynthesis  Photosynthesis produces oxygen as a waste product  Over millions of years the atmosphere filled to it’s current levels of oxygen

4. WHAT ELSE IS IN THE ATMOSPHERE: WATER VAPOR, OZONE AND DUST Water vapor enters the air through evaporation and transpiration Ozone - a molecule of oxygen that has 3 oxygen atoms (O 3 )  Forms when ultra violet (UV) rays act on oxygen in the upper atmosphere  Ozone absorbs 99% of harmful UV rays Dust includes tiny grains of rock, dirt, pollen, soot, chemicals and bacteria

5. ATMOSPHERIC PRESSURE: The pressure exerted on a surface by the atmosphere Decreases as altitude increases Measured using a barometer Units of measure: Atmospheres Mm or inches of mercury Millibars 1 atmosphere = 760 mm Hg = 1000 mb

6. LAYERS OF THE ATMOSPHERE: a)Troposphere b)Stratosphere c)Mesosphere d)Thermosphere http://www.youtube.c om/watch?v=FHtvDA0 W34I

7. STRUCTURE OF THE ATMOSPHERE Divided into five layers based on temperature changes Troposphere – 0 – 18 km  Closest to the earth  Weather occurs here  Boundary of the troposphere is the tropopause Stratosphere – 18 - 50 km  Clear and dry  Contains the ozone layer  Very little water vapor

8. TROPOSPHERE: Temperature decreases as altitude increases because its heated by Earth’s surface

9. STRATOSPHERE: As altitude increases temperature increases because UV rays absorbed by ozone

10. STRUCTURE OF THE ATMOSPHERE Mesosphere – 50-80 km  Gets colder with increasing altitude  Coldest temp in atmosphere in this layer (-80°C) Thermosphere — 80-480 km  Very hot (980°C) *The Ionosphere –  in the lower thermosphere and upper mesosphere  where electrically charged ions are formed  These ions reflect radio signals back to earth

11. AURORA BOREALIS http://www.youtube.com/watch?v=MfPXLfkmQss

12. MESOSPHERE: Temperature decreases as altitude increases

13. THERMOSPHERE: As altitude increases temperature increases because oxygen and nitrogen atoms absorb solar radiation

14. EXOSPHERE – ABOVE 500KM  Outermost layer of atmosphere  Very few gas particles  No clear boundary between exosphere and space  Very low temperature