Q.O.D.

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% H2O vapor, 10% CO2, 5 to 7% H2SO4, and small amounts of N, CO, H, CH4, 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, O2, H2O, N) begins to cycle as it does today between the atmosphere, hydrosphere, biosphere and geosphere.

7. Atmospheric Gases • Nitrogen (N2)= 78% • Oxygen (O2 ) = 21% • Argon (Ar) = 0.9% • Carbon Dioxide (CO2) = 0.04% • absorbs heat in the atmosphere • All others = trace amounts

8. Atmospheric Gases

9. Atmospheric Gases • Water vapor (H2O) • variable amounts (0-4% of volume) • absorbs heat in the atmosphere • Ozone (O3) • needed in upper atmosphere but is a toxic pollutant when in the lower atmosphere • Can be harmful to plants, humans

10. Aerosols • Solids: Dust, smoke, pollen, salt, ice… • Liquid: water • Importance: • Seeds for clouds • Absorb or reflect solar radiation • 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 currents • Rising 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 troposphere • Sub-polar and sub-tropical • Contains the ozone layer • 3 O2 + UV  2 O3 • Chemical Reaction absorbs most of the UV radiation from the sun • Thickest 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 O2 and N2 absorbing high-energy radiation • contains the ionosphere – a layer of electrically charged particles • Divert cosmic radiation away from the equator toward the poles • Aurora 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. Atmospheric Temperatures • 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 gases • Hot air is less dense  rises • Radiation = ALL objects emit EM waves • Does not need a medium (i.e. sun energy to Earth) • Hotter 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) • N2 is poor absorber of radiant energy • O2 and O3 are good absorbers of UV energy • CO2 and H2O are good absorbers of infrared • None of the gases are good absorbers of visible light

23. Incoming Solar Radiation