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, 1034 -1039 (2008) Published by AAAS

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

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.

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

After Jenkyns et al. (2002)

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

Quan et al., Global Biogeochem Cycles, in press

Is there evidence in the paleorecord?

Godfrey and Falkowski, in press

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

Falkowski, Fenchel and Delong, Science, 2008 H2 or C-mediated Photosynthesis O2 Mn4+ NO3- N2 Fe3+ SO42- CO2 H2O Mn2+ NH4+ Fe2+ HS- CH4 H2 [CH2O] +CO2 Respiration O2-mediated Mn -mediated Fe-mediated S-mediated N-mediated N2-fixation Falkowski, Fenchel and Delong, Science, 2008