Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks

Details Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks

Feb 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008asbio...8..187s&link_type=abstract

Astrobiology, Volume 8, Issue 1, pp. 187-203.

Biology

Cyanobacteria, Methane Greenhouse, Pco2, Temperature Constraints

Scientific paper

Apparent cyanobacterial emergence at about 2.8 Gya coincides with the negative excursion in the organic carbon isotope record, which is the first strong evidence for the presence of atmospheric methane. The existence of weathering feedbacks in the carbonate-silicate cycle suggests that atmospheric and oceanic CO2 concentrations would have been high prior to the presence of a methane greenhouse (and thus the ocean would have had high bicarbonate concentrations). With the onset of a methane greenhouse, carbon dioxide concentrations would decrease. Bicarbonate has been proposed as the preferred reductant that preceded water for oxygenic photosynthesis in a bacterial photosynthetic precursor to cyanobacteria; with the drop of carbon dioxide level, Archean cyanobacteria emerged using water as a reductant instead of bicarbonate (Dismukes et al., 2001). Our thermodynamic calculations, with regard to this scenario, give at least a tenfold drop in aqueous CO2 levels with the onset of a methane-dominated greenhouse, assuming surface temperatures of about 60C and a drop in the level of atmospheric carbon dioxide from about 1 to 0.1 bars. The buildup of atmospheric methane could have been triggered by the boost in oceanic organic productivity that arose from the emergence of pre-cyanobacterial oxygenic phototrophy at about 2.83.0 Gya; high temperatures may have precluded an earlier emergence. A greenhouse transition timescale on the order of 50100 million years is consistent with results from modeling the carbonate-silicate cycle. This is an alternative hypothesis to proposals of a tectonic driver for this apparent greenhouse transition.

Affiliated with

Also associated with

No associations

Rating

Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cyanobacterial Emergence at 2.8 Gya and Greenhouse Feedbacks will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1316798