Primitive atmospheres . Most planets originally had a primitive atmosphere, having solar abundances of volatiles, enriched in hydrogen. Most of the hydrogen escaped into the solar nebula, leaving heavier gases such as argon, neon, and ammonia concentrated toward the surface. B. Secondary atmospheres. Secondary atmospheres are produced by outgassing from the interior of planets.
Volcanic gasses account for most of the Earth's current atmosphere.
The time duration of this reducing atmosphere is not well known, but it was probably short. Higher temperatures on Venus contributed to the photodissociation of H 2 O, removing it from the atmosphere. The enriched N 2 content of Earth is difficult to explain without biological processes. Mars volatiles are difficult to inventory until the amount of water included in permafrost is known. Structure of Atmospheres.