The Great Oxidation Event
Earth's early atmosphere contained hardly any oxygen but relatively large amounts of carbon dioxide and possibly methane, experts believe. Then during the so-called Great Oxidation Event about 2.3 to 2.5 billion years ago, oxygen levels in the atmosphere rose from vanishingly small amounts to modestly low concentrations.
"This important transition enabled a widespread diversification and proliferation of metabolic strategies and paved the way for a much later climb in oxygen to levels that were high enough to support animal life," Colman says.
The processing of carbon monoxide by the microbial community could have influenced atmospheric chemistry and climate during the Archean, an interval of Earth's history that preceded the Great Oxidation Event.
Previous computer simulations rely on a primitive biosphere as the sole means of removing near-surface carbon monoxide produced when the sun's ultraviolet rays split carbon dioxide molecules. This theoretical sink in the biosphere would have prevented substantial accumulation of atmospheric carbon monoxide.
"But our work is showing that you can't consider microbial communities as a one-way sink for carbon monoxide," Colman says. The communities both produce and consume carbon monoxide. "It's a dynamic cycle."
Colman's calculations suggest that carbon monoxide may have nearly reached percentage concentrations of 1 percent in the atmosphere, tens of thousands of times higher than current concentrations. This in turn would have exerted influence on concentration of atmospheric methane, a powerful greenhouse gas, with consequences for global temperatures.
Furthermore, such high carbon monoxide concentrations would have been toxic for many microorganisms, placing evolutionary pressure on the early biosphere.
"A much larger fraction of the microbial communi
|Contact: Steve Koppes|
University of Chicago