HR: 11:35h
AN: B52A-06    [Abstracts]
TI: Rubisco and Atmospheric Oxygen: the Archean Record.
AU: * Nisbet, E G
EM: e.nisbet@gl.rhul.ac.uk
AF: Department of Geology, Royal Holloway, Univ. of London Egham, Surrey, TW20 0EX, United Kingdom
AU: Grassineau, N V
EM: n.grassineau@gl.rhul.ac.uk
AF: Department of Geology, Royal Holloway, Univ. of London Egham, Surrey, TW20 0EX, United Kingdom
AB: Carbon isotopic evidence, from c.2.9 Ga stromatolites from Steep Rock, Ontario, Canada, c.2.9 Ga stromatolites from Mushandike, Zimbabwe, and from 2.7 to 2.65 Ga stromatolites in the Belingwe belt, Zimbabwe, implies that in all three localities the reef-building autotrophs included organisms using Forms I and II Rubisco. This inference, strong though not conclusive, is supported by other geochemical evidence that these stromatolites formed in oxic conditions. Collectively, the implication is that oxygenic photosynthesisers were present c.2.9 Ga ago, and abundant 2.7-2.65 Ga ago. Rubisco specificity and compensation may explain the paradox that, despite the inferred evolution of oxygenesis c.2.9 Ga ago, the air was anoxic in much of the Late Archaean. The Earth System may be bistable under the warming Sun, with liquid oceans occurring in either anoxic greenhouse (H2O with abundant CH4 plus CO2, but no O2) or oxic (H2O with more abundant CO2, free O2 but little CH4) states. Build-up of a very high atmospheric inventory of CO2 in the c.2.3 Ga glaciation and subsequent oxygenesis to the Rubisco CO2 compensation line may have allowed the atmosphere to reach stability in an oxygen-rich system. Since then, Form I Rubisco specificity and consequent compensation limits may have maintained the long-term atmospheric disproportion between O2 and CO2, which is now close to both CO2 and O2 compensation barriers.
DE: 0325 Evolution of the atmosphere (1610, 8125)
DE: 0330 Geochemical cycles (1030)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0448 Geomicrobiology
SC: Biogeosciences [B]
MN: 2007 Fall Meeting