Two . . . meteorites . . . called Murchison and Lonewolf Nunataks 94102, contained a trove of nucleobases, including those also found in DNA. But these meteorites also held . . . related but exotic nucleobases never seen before, said Michael Callahan, the NASA scientist who analyzed the space rocks. Analysis of dirt and ice found near the meteorites showed no evidence of these exotic nucleobases. Scientists also have found other building blocks of life — most notably amino acids, the links that form proteins — inside meteorites.
The case for extraterrestrial life just got a little stronger. If the building blocks for life are floating around in space in a concentrated way, then the task of making the final step to combine them in a way that gives rise to life seems less daunting, a bit like randomly assembling legos instead of randomly assembling a model airplane.
Query what would happen if we tried to create life forms in the lab that had these exotic nucleotides substituted for the four that we know and love.
I'll also mention (and track down the link sometime if I can), an information coding efficiency argument made by a physics blogger who is also an electrical engineer for why DNA has four nucleotides, rather than some other number. Hence, even if there are more possible nucleotides, there might be good fundamental reasons that our DNA doesn't utilize them all.