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Late Paleozoic Hyperoxia

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posted by James St. John alias James St. John on Sunday 30th of August 2015 05:31:57 AM

These are my personal notes taken during a geology presentation. I give them here because they may be of some interest. Do not expect the notes to always be in complete sentences, etc. ----------------------------------- Late Paleozoic Hyperoxia Presented by: Robert Berner (Department of Geology & Geophysics, Yale University, New Haven, Connecticut, USA) ( ( 26 April 2001 ---------- Presenting arguments for an interval of time during the Permo-Carboniferous of high atmospheric oxygen levels (hyperoxia). Evidence for this is from: 1) abundance of organic carbon and pyrite sulfur in sedimentary rocks over time 2) mass balance equations based on carbon & sulfur isotope records 3) Late Paleozoic insect gigantism 4) plant fossil carbon isotopic fractionation 5) burning experiments not definitive Organic matter burial & weathering: CO2 + H2O CH2O + O2 This equation going to the right is photosynthesis. This equation going to the left is respiration (organic matter being oxidized). Need net photosynthesis in order for O2 accumulation with organic matter burial going on. Sedimentary pyrite formation & weathering: 2Fe2O3 + 16H+ + 8SO4- leads to 15O2 + 4FeS2 + 8H2O [2 hematite molecules + 16 hydrogen ions + 8 sulfate ions leads to 15 oxygen molecules + 4 pyrite molecules + 8 water molecules] Many intermediate reactions are in this equation. For example, oxygen does not bubble out with pyrite precipitation. Bacterial sulfate reduction is a necessary process here. The equation shows formation of pyrite and generation of O2. The reverse of this equation is pyrite weathering (easily grasped, compared with the forward aspect of equation). Fractionation goes up if land plants & plankton are grown in high O2 conditions. Dragonflies ([email protected]/19842921008) grown at 35% O2 (rather than 21%) have higher metabolisms and fly better. There is a 25% increase in the size of Drosophila embryos ( if they are grown in high O2 conditions. Only the Permo-Carboniferous was a time of giant insects. 30-38% O2 estimates for the Permo-Carboniferous. People object to this idea because they think forest fires would go nuts if there were such high atmospheric O2 levels. The experiments upon which this claim is based involve sparks on strips of paper (not a good representation of the biosphere!). New experiments of forest fire susceptibility in high O2 conditions show that some trees won’t burn at 35% O2. So, this is not an valid objection. We do find charcoal then - there were forest fires. But, O2 levels were not restricted to <25% O2. Conclusion: the Permo-Carboniferous was a time of high O2 and low CO2. --------------------

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  • Published 08.20.22
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