|QUOTE (playaindahood @ Monday, Oct 3 2011, 22:16)|
| I think we can use our own planet as an indicator. |
If Earth was a random planet we stumbled upon, yes, we could. In fact, if we only ever stumbled upon Earth, and we found life on it, we'd estimate the odds of a random habitable planet having life at whooping 2/3. There would be quite a bit of uncertainty on that estimate, but it'd be an estimate.
Unfortunately, you have to deal with conditional probabilities here. The odds that a random habitable planet has life is some probability p that we're after. Given sample of one such planet, or better more, we can estimate p. But the odds of a habitable planet having life on it, given that you originated from that planet, is 100%. You can't be a life form from Earth wondering about possibility of life elsewhere if there is no life on Earth.
Let me put it in a slightly different perspective. No matter how improbable life in the universe is, and even if there is just one planet that by some miracle happened to have life on it, you'd still be from a habitable planet by definition. So the fact that you found life on Earth gives you no new information.
Earth is the one planet you can't use for statistical analysis at all. Find any
other planet with life, and we're in business. Until then, we cannot say absolutely anything about life in the rest of the universe.