Post-script: I left out the word "quickly" when I said self-replicating fuel. Obviously, carbon-based fuels have their origin in living things that can self-replicate. It's just that they self-replicate too slowly to meet our needs. What I'm saying is that, one day, we are going to produce a ready-to-use fuel that is self-generating; that can produce more of itself in a reasonably short amount of time, like bacteria. Using it to power our machines will probably still cause pollution, though. So while it doesn't solve the problem of a dirty earth, it does solve the problem of having to dig into the earth for oil using expensive equipment.

The more I think about it, the more gruesome it sounds. How do we store it? And who has the right to make it -- can households make their own fuel, or is it something that only governments can do? What if we're unable to control production and it gets out of hand?