06-26-2015, 04:36 AM
(This post was last modified: 06-26-2015, 04:36 AM by stevebowers.)
Note that Earth probably had a primary atmosphere at some point, probably long before the impact that formed the Moon. This consisted largely of H/He, but was rapidly lost by Jeans escape and sputtering (any last remnants, including primordial neon, were lost in the Moon-forming event, I think).