Don't think oxygen is required at all, but its what we have the most experience at working with though life forms not requiring oxygen are known.
As for radio, that isn't requiste either, but I think it helps us get some small advantage for now. Electromagnetic radiation, which includes radio, is throughout the parts of the universe we have been able to survey, thats how we've surveyed most of it. Since we do use electromagnetic radiation to examine and communicate it makes reasonable sense that we are going to be best at it and therefore have the most likely chance of finding coherent signals indicative of "life" using that technique. We are biased to being able to communicate with other life forms, if they exist, using techniques we are familiar with.
mole
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mole
Who is John Galt?
