History, Structure and Composition of the

Atmosphere

Earth’s Atmosphere

Extends from the Earth’s surface to outer space. About 900 km (560 miles)

Mixture of gases, solids, and liquids

Timeline – The first Atmosphere

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

N2

78%

O2

21%

CO2

0.04%Ar0.9% Other

0.06%

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

Structure of the Atmosphere

Atmospheric layers based on temperature differences

Warm layers contain gases that easily absorb the radiant energy

Cool layers contain gases that do not absorb the radiant energy

Troposphere

0 to 12 km Means air “turns over” Contains 75% of the atmospheric gases Weather, clouds, smog 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 Streams

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

Reaction absorbs most of the incoming UV radiation

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

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 = 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 bounces off of the gas and aerosols 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 Radiation

What happens toIncoming Solar Radiation?

What heats the atmosphere?

Visible light is absorbed by

land and water but reflected

by snow and ice

The absorbed visible light is

re-radiated back into the

atmosphere as longer

wavelength infrared radiation

Greenhouse gases absorb

heat energy

H2O, CO2, CH4, N2O

Differential Heating of Earth’s Surface