Paper: Early anaerobic metabolisms

Philosophical Transactions of the Royal Society B: Biological Sciences
ISSN: 0962-8436 (Paper) 1471-2970 (Online)
Issue: Volume 361, Number 1474 / October 29, 2006

Pages: 1819 - 1836
DOI: 10.1098/rstb.2006.1906
Special Issue: Discussion Meeting Issue 'Conditions for the emergence of
life on the early Earth' organized by S. Leach, I. Smith and C. Cockell

Early anaerobic metabolisms

Don E. Canfield AFF1, Minik T. Rosing, Christian Bjerrum

Abstract:
Before the advent of oxygenic photosynthesis, the biosphere was driven by
anaerobic metabolisms. We catalogue and quantify the source strengths of the
most probable electron donors and electron acceptors that would have been
available to fuel early-Earth ecosystems. The most active ecosystems were
probably driven by the cycling of H2 and Fe2+ through primary production
conducted by anoxygenic phototrophs. Interesting and dynamic ecosystems
would have also been driven by the microbial cycling of sulphur and nitrogen
species, but their activity levels were probably not so great. Despite the
diversity of potential early ecosystems, rates of primary production in the
early-Earth anaerobic biosphere were probably well below those rates
observed in the marine environment. We shift our attention to the Earth
environment at 3.8Gyr ago, where the earliest marine sediments are
preserved. We calculate, consistent with the carbon isotope record and other
considerations of the carbon cycle, that marine rates of primary production
at this time were probably an order of magnitude (or more) less than today.
We conclude that the flux of reduced species to the Earth surface at this
time may have been sufficient to drive anaerobic ecosystems of sufficient
activity to be consistent with the carbon isotope record. Conversely, an
ecosystem based on oxygenic photosynthesis was also possible with complete
removal of the oxygen by reaction with reduced species from the mantle.

Source: The Royal Society
http://www.journals.royalsoc.ac.uk/link.asp?id=R20X45523W73217Q

Posted by
Robert Karl Stonjek


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