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Published: Wednesday 11 September, 2013

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Top of pageThe quantification of greenhouse gases present in the Archaean atmosphere is critical for understanding the evolution of atmospheric oxygen, surface temperatures and the conditions for life on early Earth. For instance, it has been argued1, 2, 3, 4 that small changes in the balance between two potential greenhouse gases, carbon dioxide and methane, may have dictated the feedback cycle involving organic haze production and global cooling. Climate m michael kors outlet store prices odels have focused on carbon dioxide as the greenhouse gas responsible for maintaining abovefreezing surface temperatures during a time of low solar luminosity5, 6. However, the analysis of 2.75billionyear Gyrold7 palaeosols samples preserved in the geologic record recently provided an upper constraint on atmospheric carbon dioxide levels well michael kors outlet store prices below that required in most climate models to prevent the Earths surface from freezing. This finding prompted many to look towards methane as an additional greenhouse gas to satisfy climate models1, 4, 8, 9. Here we use model equilibrium reactions for weathering rinds on 3.2Gyrold river gravels to show that the presence of ironrich carbonate relative to common clay minerals requires a minimum partial pressure of carbon dioxide several times higher than presentday values. Unless actual carbon dioxide levels were considerably greater than this, climate models5, 6, 8 predict that additional greenhouse gases would still need to have a role in m michael kors outlet store prices aintaining abovefreezing surface temperatures.



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Photosynthetic microbial mats in the 3,416Myrold oceanNature Letters to Editor 30 Sep 2004Nature News. michael kors outlet store prices

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