[troutman]

http://m.nautil.us/issue/80/aliens/d...re-dna-with-et

In the 1980s, the biologist David Dreamer used carboxylic acids extracted from the famous Murchison meteorite to demonstrate that these simple molecules would spontaneously form cellular membranes when added to water. According to Cockell, this suggests that the ingredients for cellular life are “strewn throughout the Solar System in carbon-rich rocks,” which means “we might expect the molecules of cellularity to form in any primordial cloud, ready to deliver their cargo of protocell material to the surface of any planet with a waiting abundance of water.” Later experiments demonstrated that meteorites are far from the only source of molecular material that can form cellular membranes, suggesting that this mode of organization is likely common in the universe.

One of the most remarkable features about DNA is that it is composed of only four nucleotides—adenine, thymine, cytosine, and guanine—that can only combine in very limited ways: adenine pairs with thymine and cytosine pairs with guanine. Is the fact that there are only four nucleotides or that they combine into two base pairs an evolutionary accident? Might an extraterrestrial intelligence have a genetic code built from six or more nucleotides, and might these nucleotides be different from the four that comprise the DNA of life on Earth? This is a possibility, of course, but there are strong reasons to believe that it is unlikely.