Well Dan, I do believe you when you point out that the Earth has been bombarded by CME's, but when you say "before there was life" I can only assume you mean 'life on Earth". (If you know that there is no life anywhere else in the universe, then please tell me where you obtained the evidence.)
I also agree with you that the 'pressure' is extremely low up in that area, but the knowledge that I do not have is 'how many of the fast moving particles DO escape into space'. If you have figures (or even estimates) based on studies that have been done in that area, then again, please let me know.
I also agree with you on the fact that the 'lost' particles are 'replaced', and 'how' they are replaced is what I alluded to in the 'story' about the missing water. I know that UV radiation can break down water molecules into hydrogen and oxygen atoms. Also I now know that hydrogen and oxygen are escaping through the 'polar fountain' as described in the NASA article. Putting that information together suggests that the UV and other high-energy radiation that exists there convert the atmospheric moisture that gets into the upper atmosphere into hydrogen and oxygen. The atmospheric moisture is replaced by the evaporation of water from the surface. So, in effect the quantity of water is diminishing from the Earth. How fast that action is or how long it will take for the condition to become 'critical for life' is only a guess until some facts about the quantity of particles 'that escape' can be obtained. It may take millions of years for the Earth to become 'critical' or it may become critical with in a few years.
Perhaps the planet Mars lost most of its water in this manner.
Cheers ;-)
Johannes