As far as xenobiology is concerned, I think Huevos Grandes might be wrong; on our world twenty amino acids are coded for in DNA; but more that a hundred different amino acids have been discovered, some only in meteorites (carbonaceous chondrites), and apparently there might be billions of possible examples.
On our world the evolution of RNA and DNA replication obviously caused the selection of lifeforms containing these twenty acids.
But before self-replication emerged, life-like organic processes must have existed for an unknown time; we might find worlds where self-replication through DNA never evolves, and on those worlds the many other possible amino acids might be found. It may even be the case that other forms of self replication might emerge, not using RNA/DNA at all;
such life, if possible, could potentially utilise many amino acids not used on Earth.
I don't think that anything we know currently can rule this possibility out, but by all means prove me wrong.
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