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

Atmospheric Gases Water vapor (H2O) Ozone (O3) 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