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Atmosphere ch 17 - TheAtmosphere .6to4.0bya H&...

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The Atmosphere
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The first atmospheres – 4.6 to 4.0 bya H & He that quickly boiled or were blown away Rain of comets & C-rich bolides Continuous rain for almost 800 millions years Carbonate and carbon objects form CO2 Ice melted to water  Comet tails – frozen ammonia –forms nitrogen  
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When life began – 4.0 to 2.6 bya Outgassing – escaped from mantle through volcanic  eruptions volatiles dissolved in magma that evoke on eruption Hadean Eon gas models linked to core formation and mantle  composition Miller-Urey experiment – on premise that early atmosphere  was CH 4 , NH 4 , H 2 , H 2 O, formed amino acids under  “primitive” conditions Premise has been called into doubt – most now believe  Hadean atmosphere was CO 2 , N 2 , H 2 O
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Studies of ancient rocks show that the early  atmosphere was oxygen poor Photosynthesis –process by which organisms  convert water & CO 2  to organic sugars, releasing O 2   as a by-product Cyanobacteria – simple, blue-green algae First Great Oxidation Event – 2.4bya oxygen began  to accumulate in the atmosphere
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System interactions affecting the Hadean  atmosphere Geosphere-atmosphere interaction O 2  dissolves in water, as does Fe When Fe is present, O reacts to form solid iron oxides Without much O 2 , early dissolved Fe was high As O 2  levels rose, FeO came out in layers as banded iron  formations (BIFs) 90% of Fe used comes from BIFs, formed 2.6 to 1.9 billion  years ago
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Mesabi Range, northern Minnesota 
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System interactions affecting the Hadean  atmosphere Biosphere – atmosphere interactions Early on H 2  + O 2  produced water, removing H 2 Later, bacteria removed H 2
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