Diversity of extraterrestrial purine and pyrimidine in carbonaceous meteorites

The only sound theory is that the thing precluding life from appearing a second time, is.. life. Primitive proto-life forms or even life precursors, are probably uncompetitive in a world where soil is saturared with bacteria/archae and they must be eaten as soon as those new life forms comes to existence. Because of the rareness of the event, it would still be undetectable for humans. Pluricellular life has appeared multiple time independently though. Another theory is that life has appeared multiple time on earth out of dead matter, however the only possible design on earth would be identical (classic cell with a membrane and more strikingly, with the same base gene PGCD). It's true that some genes are universally shared and while a base 2 coding scheme can encode a functionally equivalent algorithm in many different ways, the efficiency constraints of having the shortest (accelerate division time) or most stable solution would explain the uniformity. Except this explanation is weak if we assume (to be verified) there is a consistent universal DNA pgcd that is bit perfect. And the time to divide seems like a weak argument considering the amount of dark non coding DNA, except if those constraints would only apply to primitive single celler organisms.