Re: Assumption detected
"And one species' pollutant may be another's breathing mix"
The indicator of life in a planetary atmosphere is likely to be an unexplainable oxidising agent - on the basis that these can generally only exist if something is maintaining production.
Oxygen is the logical one but there are other candidate gases and even if the life isn't air-breathing it's likely that such gasses will build up anyway. (eg, diffusing from oceans into the air, as probably happened on Earth)
The oxygenation of our atmosphere was definitely a case of the statement above, being a byproduct of plant activity and highly toxic to just about everything that existed at the time (causing the first great extinction).
I'd be happy if we picked up possible life signatures. Even assuming a CEB would be visible around any exoplanets, the odds of a spacefaring civilisation being within the range that we've seen exoplanets so far seems pretty unlikely. We can (so far) only detect exoplanets out to about 600 light years and the galaxy is over 100,000 light years across, so searches are par with being in a large dark room with a feeble flashlight only able to illuminate things a couple of feet away, looking for a black cat.
Biting the hand that feeds IT
