Life only arose once on Earth?

So, I’m reading Life, Richard Fortey’s book on paleontology, and also looking on the web to expand my knowledge. Anyway, it seems that a fundamental assumption of evolutionary biology is that life only arose once and everything else proceeded from there forward. I can understand how the mechanics of evolutionary theory mean that everything must point back to a single starting state, but why is that so? In other words, what in the early days of our planet prevented multiple geneses? Wouldn’t it be possible for the organic chemical reactions that produced the first amino acids to have happened more than once, in multiple locations? Or, similarly, for the formation of RNA and other building blocks of life? Would we be able to tell the difference today if that is indeed what happened? Or am I just confused?

No, I don’t think you’re confused. A multiple genesis scenario is possible, as is another your question prompted in my mind, that being life beginning and then dying out, and then starting again.

This is only a WAG but I don’t think there is anything prohibiting ‘multiple genesis’. To me it just suggests that such a moment is a rare and unlikely occurrence such that the chances of having two such events relatively close together (meaning thousands of years) is very slim.

Once our lifeline (so to speak) got started it quickly dominated. Who knows…maybe genesis moments have happened since but were soon swallowed by a passing minnow so never really got off the ground.

Duplicate thread. See http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=198859