From my own investigations I am far more confident that "life like earth's" (defined molecularly) is very likely to be nearly the only kind in the universe. I would argue that the use of complementary purines and pyrimidines, two memory molecules, some medium-sized inventory of amino-acid-backboned polymers of approximately the same set of hydro- philic, phobic and catalytic arms is the best solution which optimizes both easily synthesized molecules of readily available feed stocks easy made in oceanic soups or cosmic clouds and the right combination of not-too-easy and not-to-hard bonds to break and the same inventory of metal catalysts will more or less inevitably emerge as the least-effort most-abundant-resources solution. All "alternative chemistries" I've heard of break any of the following: memory molecules which are too easy or too hard to break to best serve their function and/or require less abundantly naturally pre-bioticly synthesized feed stocks. I would like to hear Dr. Cronin or someone similar respond to this.