1. 1 Evolution of Oxygen in the Atmosphere “Early” reactions driven by high energy sunlight H 2 O --- h  H + OH CO 2 --- h  CO + O Recombination reactions 2OH -----> H 2 O + O 2O -- M ---> O 2 2H -- M --> H 2 (H 2 can be lost to space) 2H 2 + O 2 -----> 2H 2 O This was a minor process!

2. 2 To produce large amounts of O 2 we need LIFE BUG + 132 O 2 Sunlight What regulates the global Oxygen concentration?

3. 3 Global scale oxygen feedback loop O2O2

4. 4 O2O2 Deep, Cold, O 2 -rich Water

5. 5 Global scale oxygen feedback loop O2O2 Deep, Cold, O 2 -rich Water Respiration

6. 6 “Correct” Atmospheric Oxygen Photosynthesis = Respiration Too Little Atmospheric Oxygen Photosynthesis >> Respiration Too Much Atmospheric Oxygen Photosynthesis << Respiration Feedback on Atmospheric O 2

7. 7 The rate of photosynthesis = respiration = 5 x 10 15 mol/yr. The atmosphere is 20% oxygen, or 3.8 x 10 19 mol. How fast is O 2 cycling in the environment?

8. 8 The rate of photosynthesis = respiration = 5 x 10 15 mol/yr. The atmosphere is 20% oxygen, or 3.8 x 10 19 mol. Residence time for oxygen = 7600 years What does this mean?? Oxygen is well mixed in the atmosphere! How fast is O 2 cycling in the environment?

9. 9 Nitrogen was outgassed early in Earth formation and constitutes 80% of the atmosphere. (1.4 x 10 20 moles) Two major sinks: – –N 2 (g) + O 2 (g) -----  T ----> 2 NO(g) – –N 2 (g) + 3H 2 (g) ----  T, catalyst ---> 2 NH 3 (g) – –Total flux = 4.6 x 10 12 moles/year Residence time = 3 x 10 7 years Nitrogen in the atmosphere

10. 10 Source: http://www.esrl.noaa.gov/gmd/ccgg/trends/

11. 11 CO 2  Mass in the atmosphere 700 Gt  Annual flux to the atmosphere is about 150 Gt  Residence time = 5 years  Does this make sense with observed CO 2 ?

12. 12 Major Constituents of the Atmosphere (atm.) N 2 0.781 O 2 0.209 Ar0.0093 CO 2 0.00035 What about WATER? Variable concentration 0 - 0.05 atm

13. 13 p(H2O) = p(saturation)*(%RH)/100 Average amount of water = 7 x 10 14 mol. average flux = 2.5 x 10 16 mol/yr residence time = 10 days Water is poorly mixed! Temperature --> (oC)

14. 14