Things like this always make me think of Sam's Archive's "Geocide" page. Which, by the way, points out that this does not in fact bring about the destruction of the Earth: http://qntm.org/destroy
There's another site called "Exit Mundi" that has a lot of doomsday scenarios. In particular, the grey goo problem: http://www.exitmundi.nl/graygoo.htm
Things like this always make me think of Sam's Archive's "Geocide" page. Which, by the way, points out that this does not in fact bring about the destruction of the Earth: http://qntm.org/destroy