Okay, we have a pretty major piece of news for you today. It turns out "geocide" isn't a word.
You may have already known that. In fact, I already knew it, because I actually made it up myself, there being no word I could find that meant "destruction of Earth". However, it turns out I didn't look hard enough. There is such a word already: "mundicide".
What I've done, see, is mix up my ancient languages. The suffix "-cide" as in "kill" or "destroy" is from Latin, but the prefix "geo-" as in "Earth" is from ancient Greek. Clearly, Latin should go with Latin here, and in Latin, "Earth" is indeed "Mundi". Unfortunately "geo-" is a much more well-known word than "mundi" - at least, I'd heard of the one but not the other - hence my error.
So basically, "geocide" is not the right word, and "mundicide" is. Apologies to everyone who I misled, and extra special thanks to Tom Wright for bringing this most glaring of errors to my attention.