"It has often been said that, if the human species fails to make a go of it here on Earth, some other species will take over the running. In the sense of developing high intelligence this is not correct. We have, or soon will have, exhausted the necessary physical prerequisites so far as this planet is concerned. With coal gone, oil gone, high-grade metallic ores gone, no species however competent can make the long climb from primitive conditions to high-level technology. This is a one-shot affair. If we fail, this planetary system fails so far as intelligence is concerned. The same will be true of other planetary systems. On each of them there will be one chance, and one chance only. (Hoyle, 1964; emphasis added)"

Quote from cosmologist Sir Fred Hoyle on this page about the "Olduvai Theory".

The gist seems to be that, in effect, if we screw all this up, that no other high industrial civilizations could follow us. At least, not for a LONG LONG time. And if we don't make the jump from a petroleum economy, then we're screwed, because there's a finite amount of the stuff and it's running out, and our using the stuff is screwing up the environment.