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Composition And Origin
Earth’s Atmosphere Composition And Origin
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Composition (Dry Air) Nitrogen (N₂) 78.08% Oxygen (O₂) 20.95% Argon (Ar) .93% Carbon Dioxide (CO₂) .03% Trace amounts of: Neon, Helium, Ozone, Krypton, Hydrogen, Methane, Carbon Monoxide, and others. (Wet Air) Amount of Water Vapor varies: .1 – 3.0 %
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Origin of Earth’s Atmosphere
There are two scientific theories as to how the Earth got its atmosphere:
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1. Outgassing Gases trapped in the solid Earth were released during volcanic events and asteroid impacts
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2. Comets Comets impacted the Earth leaving the atmosphere behind (Especially H₂O)
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The Original Atmosphere
The early atmosphere, Due to the volcanic outgassing was poisonous containing large amounts of Methane (CH₄), Ammonia (NH₃)
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Transition to our Current Atmosphere
As there was no ozone layer yet… Ultraviolet Sunlight broke down the methane and ammonia into Nitrogen, Carbon and Hydrogen. The Hydrogen rose to the top of the atmosphere and escaped into space The Carbon remained, some being incorporated into living things The Nitrogen remained in the Air
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So where did the oxygen in our air come from?
1. Plants release Oxygen from H₂O and CO₂ during photosynthesis
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2. UV Sunlight also broke down H₂O into Hydrogen and Oxygen
Again the hydrogen mostly escaped into space leaving Oxygen behind. Plants and UV light probably worked together to produce our ‘free’ oxygen
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