In:
Geobiology, Wiley, Vol. 5, No. 4 ( 2007-12), p. 311-335
Abstract:
The evolutionary history of oxygenesis is controversial. Form I of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in oxygen‐tolerant organisms both enables them to carry out oxygenic extraction of carbon from air and enables the competitive process of photorespiration. Carbon isotopic evidence is presented from ~2.9 Ga stromatolites from Steep Rock, Ontario, Canada, ~2.9 Ga stromatolites from Mushandike, Zimbabwe, and ~2.7 Ga stromatolites in the Belingwe belt, Zimbabwe. The data imply that in all three localities the reef‐building autotrophs included organisms using Form I Rubisco. This inference, though not conclusive, is supported by other geochemical evidence that these stromatolites formed in oxic conditions. Collectively, the implication is that oxygenic photosynthesizers first appeared ~2.9 Ga ago, and were abundant 2.7–2.65 Ga ago. Rubisco specificity (its preference for CO 2 over O 2 ) and compensation constraints (the limits on carbon fixation) may explain the paradox that despite the inferred evolution of oxygenesis 2.9 Ga ago, the Late Archaean air was anoxic. The atmospheric CO 2 :O 2 ratio, and hence greenhouse warming, may reflect Form I Rubisco's specificity for CO 2 over O 2 . The system may be bistable under the warming Sun, with liquid oceans occurring in either anoxic (H 2 O with abundant CH 4 plus CO 2 ) or oxic (H 2 O with more abundant CO 2 , but little CH 4 ) greenhouse states. Transition between the two states would involve catastrophic remaking of the biosphere. Build‐up of a very high atmospheric inventory of CO 2 in the 2.3 Ga glaciation may have allowed the atmosphere to move up the CO 2 compensation line 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 O 2 and CO 2 , which is now close to both CO 2 and O 2 compensation barriers.
Type of Medium:
Online Resource
ISSN:
1472-4677
,
1472-4669
DOI:
10.1111/gbi.2007.5.issue-4
DOI:
10.1111/j.1472-4669.2007.00127.x
Language:
English
Publisher:
Wiley
Publication Date:
2007
detail.hit.zdb_id:
2113509-5
SSG:
12
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