It seems like Moore's-law-like trend can get us to telescopes by 2050 that can detect the chemical composition of exo-planets. Significant oxygen would be a sig

It seems like Moore's-law-like trend can get us to telescopes by 2050 that can detect the chemical composition of exo-planets. Significant oxygen would be a sign, as on Earth, of ongoing chemical respiration from life - otherwise O2 would react and decay to other forms without being replenished. There would still be the possibility that the presence of oxygen was geologic in nature, and if we sampled a billion exo-planets, it's reasonable that some could have an exotic geology to cause this 'false positive'. The next step might be to look for a pattern in the carbon-cycle connected with orbits: e.g on Earth the North vs. South hemisphere have different amounts of plant life, and we see C02 wobble several ppm in summer vs. winter. Getting accurate readings of exo-planets to the ppm level might take a while for telescope technology to acheive. For these reasons, I'd say 2100 is a good estimate for when we would have the ability to sample 1B exoplanets, and promote at least one to the rank of 'strong possibility of harboring life'.