Transcript 14-1:Earth’s Atmosphere

History, Structure and
Composition of the
Atmosphere
Earth’s Atmosphere
 Extends from the Earth’s surface to outer
space.
 Mixture of gases, solids, and liquids
 About 900 km (560 miles)
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
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
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.
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
Atmospheric Gases
Ar
0.9%
CO2
0.04% Other
0.06%
O2
21%
N2
78%
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
Aerosols
 Solids: Dust, smoke, pollen, salt, ice…
 Liquid: water
 Importance:
• Seeds for clouds
• Absorb or reflect solar radiation
• Make pretty sunsets!
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
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
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
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
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
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
Exosphere
 450 to 900 km
 very little air here
 Where the space shuttle orbits the Earth
 Some orbiting satellites
Atmospheric Temperatures
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
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
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
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
Incoming Solar Radiation
Absorbed
by land
and sea
50%
Reflected
into
space
30%
Absorbed
by atmosphere
20%