Well the New Scientist reports that microbes are being found quite deep in the crust in all sorts of places. Called extremophiles, like the ones happily living around smokers (hot subsea vents).

The problemo is - we don't know what they do exactly, but if they have existed for a long time they may be doing something to the rock that makes the planet what it is, and if it ain't broke don't fix it - by destroying some of the cogs!