To completely vaporize the Earth, you'll need to overcome the Gravitational Binding Energy of all of the atoms that hold the planet together. This amounts to 224,000,000,000,000,000,000,000,000,000,000 Joules. If you are uninspired, as so many evil geniuses are (sorry guys, but you know you are), then you probably went to ThermoNuclear Depot and tried to buy some nuclear weapons to do the job. Stan, the nice guy who works in that department with the bright red vest wearing a button that says 'Get Bent', told you that it would take roughly 107,000,000,000,000 bombs to vaporize the planet (he gets about three guys a week asking for the same thing). He politely and cheerfully sends you to the Special Order department to fill out one of their forms (they don't keep that many in stock, and they are seasonal). Most evil geniuses are averse to filling out forms, so you left. Here's the math: 224,000,000,000,000,000,000,000,000,000,000 Joules per planet divided by 2,100,000,000,000,000,000 Joules per nuclear bomb = 107,000,000,000,000 nuclear bombs per planet.