Q.O.D.Where did the modern Atmosphere come

from?

History, History, Structure and Structure and Composition of Composition of the Atmospherethe Atmosphere

Earth’s Atmosphere Extends from the Earth’s surface to outer Extends from the Earth’s surface to outer

space. space. Mixture of gases, solids, and liquidsMixture of gases, solids, and liquids About 900 km (560 miles)About 900 km (560 miles)

Timeline (part 1) Hydrogen and Helium were stripped away Hydrogen and Helium were stripped away

by solar wind early in Earth’s history by solar wind early in Earth’s history Outgassing – volcanic eruptions Outgassing – volcanic eruptions First Stable AtmosphereFirst Stable Atmosphere Contained 80% HContained 80% H22O vapor, 10% COO vapor, 10% CO22, 5 to , 5 to

7% H7% H22SOSO44, and small amounts of N, CO, H, , and small amounts of N, CO, H, CHCH44, and Ar, and Ar

Second Atmosphere Water in the atmosphere Water in the atmosphere

condensed and fell to Earth condensed and fell to Earth creating oceans (3.8 Ga)creating oceans (3.8 Ga)

Very primitive single celled life Very primitive single celled life forms (3.5GA)forms (3.5GA)

Nitrogen was the predominant Nitrogen was the predominant gas (3.4 Ga)gas (3.4 Ga)

Photosynthesis began with blue-Photosynthesis began with blue-green algae (3 Ga) green algae (3 Ga)

Oxygen builds up in the Oxygen builds up in the atmosphereatmosphere

Third (Modern) Atmosphere At 2 Ga, ozone begins to form in the At 2 Ga, ozone begins to form in the

stratospherestratosphere Increasing oxygen levels stabilized at ~20% (650 Increasing oxygen levels stabilized at ~20% (650

Ma)Ma) Stratospheric Ozone was thick enough to protect Stratospheric Ozone was thick enough to protect

Earth’s surface from UV radiationEarth’s surface from UV radiation Matter (C, OMatter (C, O22, H, H22O, N) begins to cycle as it does O, N) begins to cycle as it does

today between the atmosphere, hydrosphere, today between the atmosphere, hydrosphere, biosphere and geosphere.biosphere and geosphere.

Atmospheric Gases Nitrogen (NNitrogen (N22)= 78% )= 78% Oxygen (OOxygen (O22 ) = 21% ) = 21% Argon (Ar) = 0.9%Argon (Ar) = 0.9% Carbon Dioxide (COCarbon Dioxide (CO22) = 0.04%) = 0.04%

• absorbs heat in the atmosphereabsorbs heat in the atmosphere All others = trace amountsAll others = trace amounts

Atmospheric Gases

Atmospheric Gases Water vapor (HWater vapor (H22O)O)

• variable amounts (0-4% of volume)variable amounts (0-4% of volume)• absorbs heat in the atmosphereabsorbs heat in the atmosphere

Ozone (OOzone (O33))• needed in upper atmosphere but is a toxic needed in upper atmosphere but is a toxic

pollutant when in the lower atmospherepollutant when in the lower atmosphere• Can be harmful to plants, humansCan be harmful to plants, humans

Aerosols Solids: Dust, smoke, pollen, salt, ice…Solids: Dust, smoke, pollen, salt, ice… Liquid: waterLiquid: water Importance:Importance:

• Seeds for cloudsSeeds for clouds• Absorb or reflect solar radiationAbsorb or reflect solar radiation• Make pretty sunsets!Make pretty sunsets!

Atmospheric Pressure Gravity causes gases in the atmosphere to be Gravity causes gases in the atmosphere to be

pulled toward the Earthpulled toward the Earth Weight of gases above presses down on the air Weight of gases above presses down on the air

belowbelow Density increasesDensity increases Force exerted on an area is known as Force exerted on an area is known as pressurepressure Air pressure greater near the EarthAir pressure greater near the Earth Air pressure measured by a Air pressure measured by a barometerbarometer

Structure of the Atmosphere Atmosphere divided into layers based on Atmosphere divided into layers based on

temperature differencestemperature differences Some layers contain gases that easily absorb the Some layers contain gases that easily absorb the

sun’s energy, other layers do notsun’s energy, other layers do not Therefore, each layer contains different amount of Therefore, each layer contains different amount of

energy and temperature differencesenergy and temperature differences

Troposphere 0 to 12 km (where we live…)0 to 12 km (where we live…) Means air “turns over”Means air “turns over” Contains 75% of the atmospheric gasesContains 75% of the atmospheric gases Weather, clouds, smog occur hereWeather, clouds, smog occur here Average environmental lapse rate is 6.5Average environmental lapse rate is 6.5°C per °C per

km (3.5°F per 1000 ft)km (3.5°F per 1000 ft) Hadley CellsHadley Cells

• Wind currents directly influence ocean currentsWind currents directly influence ocean currents• Rising air = cloud formation; Sinking air = dry airRising air = cloud formation; Sinking air = dry air

Stratosphere 12 to 50 km12 to 50 km Jet airplanes fly in the lower stratosphereJet airplanes fly in the lower stratosphere Jet StreamJet Stream

• a fast moving channel of air that controls the location of a fast moving channel of air that controls the location of high and low pressure cells in the tropospherehigh and low pressure cells in the troposphere

• Sub-polar and sub-tropicalSub-polar and sub-tropical Contains the ozone layerContains the ozone layer

• 3 O3 O22 + UV + UV 2 O 2 O33• Chemical Reaction absorbs most of the UV radiation Chemical Reaction absorbs most of the UV radiation

from the sunfrom the sun• Thickest at the equator, thinnest at the polesThickest at the equator, thinnest at the poles

Increasing temps above 20 kmIncreasing temps above 20 km

Mesosphere 50 to 80 km50 to 80 km temps decreasing to -90temps decreasing to -90°C°C with altitude with altitude Meteors disintegrate in this layerMeteors disintegrate in this layer Little is known about this layer because Little is known about this layer because

it is above where research balloons and it is above where research balloons and aircraft fly but below where satellites aircraft fly but below where satellites orbitorbit

Thermosphere 80 to 450 km80 to 450 km Orbiting satellitesOrbiting satellites Temps increasing with altitude because of OTemps increasing with altitude because of O22 and and

NN22 absorbing high-energy radiation absorbing high-energy radiation contains the contains the ionosphere – ionosphere – a layer of electrically a layer of electrically

charged particlescharged particles• Divert cosmic radiation away from the equator toward Divert cosmic radiation away from the equator toward

the polesthe poles• Aurora result from cosmic radiation interacting with the Aurora result from cosmic radiation interacting with the

ionosphere at the polesionosphere at the poles

Exosphere Is it really out there?Is it really out there? 450 to 900 km450 to 900 km VERYVERY little air here little air here Where the space shuttle orbits the EarthWhere the space shuttle orbits the Earth Some orbiting satellitesSome orbiting satellites

Atmospheric Temperatures

Atmospheric Temperatures As atmosphere is heated, air molecules As atmosphere is heated, air molecules

move with greater energymove with greater energy Warm air is less dense (low air pressure)Warm air is less dense (low air pressure) Cold air is more dense (high air pressure)Cold air is more dense (high air pressure)

Cool Warm

Heat & Temperature Heat = (a form of energy) Heat = (a form of energy) totaltotal kinetic kinetic

energy of the molecules in a substanceenergy of the molecules in a substance Temperature = Temperature = averageaverage kinetic energy of kinetic energy of

the moleculesthe molecules Heat Heat alwaysalways moves from high to low temps moves from high to low temps

Heat Transfer Three mechanisms of heat transfer between land, Three mechanisms of heat transfer between land,

water, and atmospherewater, and atmosphere ConductionConduction = transfer of heat through matter by = transfer of heat through matter by

molecules colliding (transfer by touching)molecules colliding (transfer by touching) ConvectionConvection = transfer of heat by circulation within = transfer of heat by circulation within

a substancea substance• Only in liquids or gasesOnly in liquids or gases• Hot air is less dense Hot air is less dense rises rises

RadiationRadiation = ALL objects emit EM waves = ALL objects emit EM waves• Does not need a medium (i.e. sun energy to Earth)Does not need a medium (i.e. sun energy to Earth)• Hotter objects emit shorter wavelengthsHotter objects emit shorter wavelengths

Incoming Solar Radiation ScatteringScattering = incoming waves can “bounce” off = incoming waves can “bounce” off

particles in the atmosphereparticles in the atmosphere ReflectionReflection = 30% of solar radiation is reflected = 30% of solar radiation is reflected

back into spaceback into space AbsorptionAbsorption = molecules absorbing energy = molecules absorbing energy

increase speed (get hotter)increase speed (get hotter)• NN22 is poor absorber of radiant energy is poor absorber of radiant energy• OO22 and O and O33 are good absorbers of UV energy are good absorbers of UV energy• COCO22 and H and H22O are good absorbers of infraredO are good absorbers of infrared• None of the gases are good absorbers of visible lightNone of the gases are good absorbers of visible light

Incoming Solar Radiation