6. AtmosEvol

6. AtmosEvol - Atmospheres and Oceans Key Questions: Why is...

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1 Atmospheres and Oceans Key Questions: Why is there air? (according to Cosby……) Other questions? What is present composition? Where did volatiles originate? What was history and how do we know this? This is a dynamic system. What regulates present composition? www.billcosby.com Present Atmosphere Composition: What are major gases? Present Composition: Major Gases and Water Major Constituents of Dry Air (%) Comments Nitrogen 78.1 Oxygen 20.9 Argon 0.93 (99.94% is 40Ar) We are the only planet with significant O2 Note that 40Ar is created by 40K decay Oceans Contains water, dissolved gas and salts Largest mass of H2O near planet surface (98%, 2% in ice caps) Minor Gases (in ppm) Gas ppm Comments greenhouse gases (affected by humans) CO 2 375 rising about 15 ppm per decade CH 4 1.8 rising about 7% per decade N 2 O 0.3 rising about 2% per decade noble gases (highly depleted compared to sun) He 5.2 can escape from earth gravity Ne 18.2 Kr 1.1 Xe 0.1 others H 2 0.5 quite reactive, can escape from earth Others (O 3 , CO, SO 2 , NO 2 , NH 3 , CFCs) <<1 ppm and quite variable Volatiles: Likely Sources Volatiles: materials vaporized at low to modest temperatures, like water, carbon dioxide, nitrogen, sulfur oxides, etc. Sources: 1. Planetary accretion! Carbonaceous chondrites (type of meteorite) have >1% H20 and much organic matter containing C and N. But how did volatiles reach the atmosphere? 338 Hadean picture volcanism releases volatiles
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2 Likely Sources of Volatiles Sources: 1. Initial Earth Accretion.
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This note was uploaded on 11/30/2010 for the course GEOL 125Lxg at USC.

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6. AtmosEvol - Atmospheres and Oceans Key Questions: Why is...

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