Post on 14-Dec-2015
transcript
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Evolution of Oxygen in the Atmosphere
• “Early” reactions driven by high energy sunlight
H2O --- h< 240 nm ---> H + OH
CO2 --- h< 240 nm ---> CO + O
• Recombination reactions
• 2OH -----> H2O + O
• 2O -- M ---> O2
• 2H -- M --> H2 (H2 can be lost to space)
• 2H2 + O2 -----> 2H2O
• This was a minor process!
22
To produce large amounts of O2 we need LIFE
BUG
+ 132 O2
Sunlight
• What regulates the global Oxygen concentration?
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AtmosphereAtmosphereContinentalContinental
CrustCrust
OceanOcean
Global scale oxygen feedback loop
O2
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AtmosphereAtmosphereContinentalContinental
CrustCrust
OceanOcean
Global scale oxygen feedback loop
O2
Deep, Cold, O2-rich Water
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AtmosphereAtmosphereContinentalContinental
CrustCrust
OceanOcean
Global scale oxygen feedback loop
O2
Deep, Cold, O2-rich Water
Respiration
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• “Correct” Atmospheric OxygenPhotosynthesis = Respiration
• Too Little Atmospheric OxygenPhotosynthesis >> Respiration
• Too Much Atmospheric OxygenPhotosynthesis << Respiration
Feedback on Atmospheric O2
77
• The rate of photosynthesis = respiration = 5 x 1015
mol/yr.
• The atmosphere is 20% oxygen, or 3.8 x 1019 mol.
How fast is O2 cycling in the environment?
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• The rate of photosynthesis = respiration = 5 x 1015 mol/yr.
• The atmosphere is 20% oxygen, or 3.8 x 1019 mol.
• Residence time for oxygen = 7600 years
• What does this mean?? Oxygen is well mixed in the atmosphere!
How fast is O2 cycling in the environment?
99
• Nitrogen was outgassed early in Earth formation and constitutes 80% of the atmosphere. (1.4 x 1020 moles)
• Two major sinks:
– N2(g) + O2(g) ----- T ----> 2 NO(g)
– N2(g) + 3H2(g) ---- T, catalyst ---> 2 NH3(g)
– Total flux = 4.6 x 1012 moles/year
• Residence time = 3 x 107 years
Nitrogen in the atmosphere
1010Source: http://www.esrl.noaa.gov/gmd/ccgg/trends/Source: http://www.esrl.noaa.gov/gmd/ccgg/trends/
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CO2
Mass in the atmosphere 700 GtMass in the atmosphere 700 Gt Annual flux to the atmosphere is about 150 GtAnnual flux to the atmosphere is about 150 Gt
Residence time = 5 yearsResidence time = 5 years Does this make sense with observed CODoes this make sense with observed CO22??
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• Major Constituents of the Atmosphere (atm.)
N2 0.781
O2 0.209
Ar 0.0093
CO2 0.00035
What about WATER?
Variable concentration 0 - 0.05 atm
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• p(H2O) = p(saturation)*(%RH)/100
• Average amount of water = 7 x 1014 mol.
• average flux = 2.5 x 1016 mol/yr
• residence time = 10 days
• Water is poorly mixed!
Temperature --> (oC)Temperature --> (oC)