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Origin of Earth’s Atmosphere Early Earth was HOT!
Why? Accretion; Radioactive decay of elements
Consequences - Constant volcanism, surface temperature too high for liquid water or life as we know it, molten surface or thin, unstable basaltic crust.
Cooling led to: Condensation & accumulation of surface water
Changing atmosphere due to volcanic out-gassing
The right conditions for the evolution of life
Source: http://www.ux1.eiu.edu/~cfjps/1400/atmos_origin.html
1st Atmosphere
Composition - H2, He
Lost to space early in Earth's history because: Earth's gravity is not strong enough to hold lighter
gases
Earth still did not have a differentiated core (solid inner/liquid outer core) which creates Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar winds.
Once the core differentiated the heavier gases could be retained
2nd AtmosphereProduced by volcanic out-gassing.H2O, CO2, SO2, CO, S2, Cl2, N2, H2 and
NH3 (ammonia) and CH4 (methane)
No free O2 at this time
Ocean Formation - As the Earth cooled, H2O produced by out-gassing could exist as liquid in the early Archean, allowing oceans to form.
The Earth in its earliest years was a horribly hot and violent place. Asteroids, comets, and other chunks of space debris left over from the solar system's formation continually bombarded the young planet, releasing huge amounts of heat, and bringing water in the form of ice to Earth.
Addition of O2Photochemical dissociation - breakup of
water molecules by UV radiation Produced O2 levels approx. 1-2% current levels
At these levels O3 (Ozone) can form to shield Earth surface from UV
Photosynthesis – CO2 + H2O + sunlight glucose + O2
O2 produced by cyanobacteria, and eventually higher plants, such as stromatolites
This process produced most of Earth’s oxygen.
Present Composition78% Nitrogen
21% Oxygen
1% Other trace gases
Layers of the Atmosphere
Caused by temp. differences
These differences result from how solar energy is absorbed as it moves through the atmosphere
http://www.aerospaceweb.org/question/atmosphere/atmosphere/layers.gif
4 Main Layers of the Atmosphere
http://www.epa.gov/apti/course422/images/fig-1.gif
http://www.greenfacts.org/images/glossary/stratosphere-troposphere.jpg
TroposphereClosest to EarthNearly all weather occurs hereAlmost all H2O vapor and CO2
Temp. decreases with altitude because air in this layer is heated from below by thermal energy that is re-radiated from Earth’s surface
Tropopause
Upper boundary of the troposphere
Jet stream
-Varies with latitude & seasons
-250 mph
-East wind
Stratosphere16 – 50 kmOzone layer is hereTemp. increases because air is heated from above by absorption of solar radiation by ozone
Jets fly here to avoid turbulenceStratopause - upper boundary
Ozone LayerOzone is made of 3 atoms of oxygen (O3)
≈ 2-3 mm thick if it were at sea level
Purpose - absorbs harmful UV radiation from the Sun
Mesosphere50 – 85 kmTemp. decreases as altitude increases
Mesopause - Upper boundaryAvg Temp. = - 90oCCOLDEST layer in the atmosphereMeteors begin to disintegrate here
Thermosphere
90 km ~ 1000 kmSpace begins here (~100 km)Temp. increases as altitude increasesCan’t read temp. with a thermometer because air particles are too far apart
Space Shuttle & ISS orbit hereIonosphere is the lower regionAurora occur here
ExosphereEnd of the atmosphere
Almost a vacuum
Where light elements escape Earth’s gravity
http://curriculum.calstatela.edu/courses/builders/lessons/less/les3/les3gifs/layers.gif