1. Q.O.D.   Where did the modern Atmosphere come from?

2. History, Structure and Composition of the Atmosphere

3. Earth’s Atmosphere  Extends from the Earth’s surface to outer space.  Mixture of gases, solids, and liquids  About 900 km (560 miles)

4. Timeline (part 1)  Hydrogen and Helium were stripped away by solar wind early in Earth’s history  Outgassing – volcanic eruptions  First Stable Atmosphere  Contained 80% H 2 O vapor, 10% CO 2, 5 to 7% H 2 SO 4, and small amounts of N, CO, H, CH 4, and Ar

5. Second Atmosphere  Water in the atmosphere condensed and fell to Earth creating oceans (3.8 Ga)  Very primitive single celled life forms (3.5GA)  Nitrogen was the predominant gas (3.4 Ga)  Photosynthesis began with blue-green algae (3 Ga)  Oxygen builds up in the atmosphere

6. Third (Modern) Atmosphere  At 2 Ga, ozone begins to form in the stratosphere  Increasing oxygen levels stabilized at ~20% (650 Ma)  Stratospheric Ozone was thick enough to protect Earth’s surface from UV radiation  Matter (C, O 2, H 2 O, N) begins to cycle as it does today between the atmosphere, hydrosphere, biosphere and geosphere.

7. Atmospheric Gases  Nitrogen (N 2 )= 78%  Oxygen (O 2 ) = 21%  Argon (Ar) = 0.9%  Carbon Dioxide (CO 2 ) = 0.04% absorbs heat in the atmosphereabsorbs heat in the atmosphere  All others = trace amounts

8. Atmospheric Gases

9.  Water vapor (H 2 O) variable amounts (0-4% of volume)variable amounts (0-4% of volume) absorbs heat in the atmosphereabsorbs heat in the atmosphere  Ozone (O 3 ) needed in upper atmosphere but is a toxic pollutant when in the lower atmosphereneeded in upper atmosphere but is a toxic pollutant when in the lower atmosphere Can be harmful to plants, humansCan be harmful to plants, humans

10. Aerosols  Solids: Dust, smoke, pollen, salt, ice…  Liquid: water  Importance: Seeds for cloudsSeeds for clouds Absorb or reflect solar radiationAbsorb or reflect solar radiation Make pretty sunsets!Make pretty sunsets!

11. Atmospheric Pressure  Gravity causes gases in the atmosphere to be pulled toward the Earth  Weight of gases above presses down on the air below  Density increases  Force exerted on an area is known as pressure  Air pressure greater near the Earth  Air pressure measured by a barometer

12. Structure of the Atmosphere  Atmosphere divided into layers based on temperature differences  Some layers contain gases that easily absorb the sun’s energy, other layers do not  Therefore, each layer contains different amount of energy and temperature differences

13. Troposphere  0 to 12 km (where we live…)  Means air “turns over”  Contains 75% of the atmospheric gases  Weather, clouds, smog occur here  Average environmental lapse rate is 6.5°C per km (3.5°F per 1000 ft)  Hadley Cells Wind currents directly influence ocean currentsWind currents directly influence ocean currents Rising air = cloud formation; Sinking air = dry airRising air = cloud formation; Sinking air = dry air

14. Stratosphere  12 to 50 km  Jet airplanes fly in the lower stratosphere  Jet Stream a fast moving channel of air that controls the location of high and low pressure cells in the tropospherea fast moving channel of air that controls the location of high and low pressure cells in the troposphere Sub-polar and sub-tropicalSub-polar and sub-tropical  Contains the ozone layer 3 O 2 + UV  2 O 33 O 2 + UV  2 O 3 Chemical Reaction absorbs most of the UV radiation from the sunChemical Reaction absorbs most of the UV radiation from the sun Thickest at the equator, thinnest at the polesThickest at the equator, thinnest at the poles  Increasing temps above 20 km

15. Mesosphere  50 to 80 km  temps decreasing to -90°C with altitude  Meteors disintegrate in this layer  Little is known about this layer because it is above where research balloons and aircraft fly but below where satellites orbit

16. Thermosphere  80 to 450 km  Orbiting satellites  Temps increasing with altitude because of O 2 and N 2 absorbing high-energy radiation  contains the ionosphere – a layer of electrically charged particles Divert cosmic radiation away from the equator toward the polesDivert cosmic radiation away from the equator toward the poles Aurora result from cosmic radiation interacting with the ionosphere at the polesAurora result from cosmic radiation interacting with the ionosphere at the poles

17. Exosphere  Is it really out there?  450 to 900 km  VERY little air here  Where the space shuttle orbits the Earth  Some orbiting satellites

18. Atmospheric Temperatures

19.  As atmosphere is heated, air molecules move with greater energy  Warm air is less dense (low air pressure)  Cold air is more dense (high air pressure) Cool Warm

20. Heat & Temperature  Heat = (a form of energy) total kinetic energy of the molecules in a substance  Temperature = average kinetic energy of the molecules  Heat always moves from high to low temps

21. Heat Transfer  Three mechanisms of heat transfer between land, water, and atmosphere  Conduction = transfer of heat through matter by molecules colliding (transfer by touching)  Convection = transfer of heat by circulation within a substance Only in liquids or gasesOnly in liquids or gases Hot air is less dense  risesHot air is less dense  rises  Radiation = ALL objects emit EM waves Does not need a medium (i.e. sun energy to Earth)Does not need a medium (i.e. sun energy to Earth) Hotter objects emit shorter wavelengthsHotter objects emit shorter wavelengths

22. Incoming Solar Radiation  Scattering = incoming waves can “bounce” off particles in the atmosphere  Reflection = 30% of solar radiation is reflected back into space  Absorption = molecules absorbing energy increase speed (get hotter) N 2 is poor absorber of radiant energyN 2 is poor absorber of radiant energy O 2 and O 3 are good absorbers of UV energyO 2 and O 3 are good absorbers of UV energy CO 2 and H 2 O are good absorbers of infraredCO 2 and H 2 O are good absorbers of infrared None of the gases are good absorbers of visible lightNone of the gases are good absorbers of visible light

23. Incoming Solar Radiation