I have posted a suggestion of contributing to Citizendium in a most-read blog of Earth scientists (
http://www.realclimate.org/), let's see what happens.
I am not sure recruitment letters are the right way to do it. This is not the usual way scientists communicate, at least in my experience. If I was to receive a recruitment letter, it would sound suspect to me (why? Don't ask, I don't know. Subtle psychologic effect, I suppose).
Anyway, the first contributors to Earth Science arrived already, and they seem to be active! This is good news. Now we need EDITORS, and many of them: Earth Science is multidisciplinary, and geology editors may know almost nothing about oceanography or atmospheric science. This is, indeed, the case right now (I am talking for myself of course!)