Some people, like Keith Henson, argue that we've blown the thermodynamic opportunity to get off planet because we've already squandered the best quality fossil fuels.

This seems very strange. First, most of our rockets use hydrogen and oxygen. One doesn't directly need to use fossil fuels. Second, there's still a massive amount of energy available in terms of fossil fuels, it just involves lower energy return on energy investment. Third of all, there are many other sources of energy, with nuclear power being one of the more obvious, but massive amounts o... (read more)