Dang it. Dan Shaw writes,
Speaking as a (failing) Classical scholar, I see no problem in persisting to call the action of destroying the Earth 'geocide'. It's true that 'mundicide' is constructed from two Latin words, but there are some examples of English words constructed from Greek and Latin, the two most notable being 'television' (pretty common usage, I believe) and 'genocide' (also unfortunately common, and analogous to 'geocide' which was the point in using it in the first place, yes?). The OED lists 'mundicidious', which is patently silly, obsolete and in fact only used over 350 years ago when inventing new and silly words was all there was to do of an evening (1647, N. Ward, Simple Cobler Aggawam [ed. 3] 20 'A vacuum and an exorbitancy are mundicidious evils').
My vote (which counts for nothing in this first-past-the-post world) is for 'geocide': it's funnier, sexier, closer to other scientific words (geology etc.) and an entirely new coinage - which would mean you'd be cited in future editions of the OED and the Ultra-Complete Maximegalon Dictionary of Every Language Ever.
PS: Perhaps the study of geocide should be 'geocidology', and you and your companions are therefore 'geocidologists'? 'Sam Hughes, Research Geocidologist' has a nice ring to it...
What do you think, folks? Mail me. I'm in two minds, as personally I prefer the word "geocide" anyway.