History, Structure and Composition of the Atmosphere

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History, Structure and Composition of the
Atmosphere
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Earths Atmosphere

• Extends from the Earths surface to outer space.
• Mixture of gases, solids, and liquids
• About 900 km (560 miles)

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Timeline (part 1)

• Hydrogen and Helium were stripped away by solar
  wind early in Earths 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

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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

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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
  Earths surface from UV radiation
• Matter (C, O2, H2O, N) begins to cycle as it does
  today between the atmosphere, hydrosphere,
  biosphere and geosphere.

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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

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Atmospheric Gases
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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

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Aerosols

• Solids Dust, smoke, pollen, salt, ice
• Liquid water
• Importance
• Seeds for clouds
• Absorb or reflect solar radiation
• Make pretty sunsets!

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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

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Structure of the Atmosphere

• Atmosphere divided into layers based on
  temperature differences
• Some layers contain gases that easily absorb the
  suns energy, other layers do not
• Therefore, each layer contains different amount
  of energy and temperature differences

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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 6.5C per km
  (3.5F per 1000 ft)
• Hadley Cells
• Wind currents directly influence ocean currents
• Rising air cloud formation Sinking air dry
  air

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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

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Mesosphere

• 50 to 80 km
• temps decreasing to -90C 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

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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

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Exosphere

• 450 to 900 km
• very little air here
• Where the space shuttle orbits the Earth
• Some orbiting satellites

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Atmospheric Temperatures
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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
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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

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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

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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

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Incoming Solar Radiation