Earth-like planets outgassed atmosphere

It seems imlikely that the Earth kept much of its earliest atmosphere drrring early accretion, thus the primordial atmosphere would have been derived from outgassing of the planet s interior, which is thought to have occurred at temperatures between 300 to 1500° C. Modem volcanoes emit a wide range of gas mixtures, most of which is CO2 and SO2, rather than CH4 and H2S. However, it seems likely that most of the gases released today are from the reactions of reworked crastal material and water, and do not represent components of the Earth s deep interior. Thus modem volcanic gases may tell us little about the early Earth s atmosphere. 

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