1. P. G. Falkowski et al., Science 320, 1034 -1039 (2008)
Fig. 1. A generalized biosphere model showing the basic inputs and outputs of energy and materials
P. G. Falkowski et al., Science 320, (2008)
Published by AAAS

2. Mn2+ NH4+ Fe2+ HS- CH4 H2 [CH2O]
H2 or C-mediated
Photosynthesis O2
Mn4+
NO3- N2
Fe3+
SO42-
CO2
H2O
Mn NH Fe HS CH H [CH2O]
+CO2
Respiration
O2-mediated
Mn -mediated
Fe-mediated
S-mediated
N-mediated
N2-fixation

4. The rise of oxygen altered the N cycle- The BIG FLIP
Oxygen permitted NH4 to be converted to NO3 – which can be rapidly reduced to N2.
There was a critical time in Earth’s history when the N cycle was a major barrier to oxidizing the planet
Once over that “hump” we entered a new stable state.

5. d34S sulfate d34S sulfide D33S
Courtesy of Farquhar et al, Science 2004

7. After Jenkyns et al. (2002)

8. Similar feedback during Oceanic Anoxic Events?
Anoxic environments:
 denitrification
 removal of fixed nitrogen from the ocean
retards of primary production, favors N2-fixers
Jenkyns et al. 2001

9. Quan et al., Global Biogeochem Cycles, in press

10. Is there evidence in the paleorecord?

12. Godfrey and Falkowski, in press

14. Evidence of lateral gene transfer of nif genes
Shi and Falkowski, PNAS 2008

15. Falkowski, Fenchel and Delong, Science, 2008
H2 or C-mediated
Photosynthesis O2
Mn4+
NO3- N2
Fe3+
SO42-
CO2
H2O
Mn NH Fe HS CH H [CH2O]
+CO2
Respiration
O2-mediated
Mn -mediated
Fe-mediated
S-mediated
N-mediated
N2-fixation
Falkowski, Fenchel and Delong, Science, 2008