Primary atmosphere primitive

We call the present atmosphere of the earth secondary , but the discussion is still open whether there was a primordial atmosphere and what the composition of the primary one was. The so-called primitive (or primordial) atmosphere could have been formed by the remaining gas phase (solar wind) from solar nebula (H2, He). However, it is unlikely that the earth had such a primitive atmosphere. There are several assumptions (e. g. the collision of earth with another celestial body, by which... 

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