Scientists said Thursday that they had trained a bacterium to eat and grow on a diet of arsenic, in place of phosphorus — one of six elements considered essential for life — opening up the possibility that organisms could exist elsewhere in the universe or even here on Earth using biochemical powers we have not yet dared to dream about. . . .Personally, I have always been mystified by scientists who think that life on other worlds has to be chemically similar to life on earth. The Viking landers took an experiment to Mars that fed the soil a broth rich in chemicals appealing to earthbound microbes, with the idea that Martian microbes would go to town on it and release lots of metabolic gases. Even as a teenager I thought this was weirdly narrow-minded; what if earth's organic compounds are actually poisonous to Martian life? Yes, I understand the unique power of organic chemistry -- I started college as a chemistry major -- but that very power can give rise to millions of different forms, most of which are not part of earthly life.
Scientists said the results, if confirmed, would expand the notion of what life could be and where it could be. “There is basic mystery, when you look at life,” said Dimitar Sasselov, an astronomer at the Harvard-Smithsonian Center for Astrophysics and director of an institute on the origins of life there, who was not involved in the work. “Nature only uses a restrictive set of molecules and chemical reactions out of many thousands available. This is our first glimmer that maybe there are other options.”
The revelations of quantum mechanics and cosmology ought to make us humble in the face of the universe's astonishing weirdness. The world is stranger than we can suppose, and when we finally do meet extraterrestrial life I expect it will be so alien to us that we will have trouble even deciding if it is alive.