Very few things are thought to be universal to all life forms on earth. One of those few things has long been the notion that all living organisms use phosphate-linked DNA as their genetic material. A NASA research team recently announced that they had discovered a bacterium that is capable of substituting arsenic for phosphorous when necessary. One bacterium in particular, termed strain GFAJ-1, was removed from California's Mono Lake, which is unique for its abnormally high levels of salt, arsenic, phosphorous, and sulfur. When this strain was cultured under even higher arsenic levels it continued to thrive and reproduce, although not as rapidly as when fed phosphorous. The most interesting result came when phosphorus levels were reduced to trace levels in the culture and GFAJ-1 continued to reproduce at levels that would not be possible if only phosphorous was being incorporated into newly synthesized DNA, indicating that arsenic was being used as a replacement during DNA synthesis.
While arsenic is not terribly different from phosphorous on a chemical level, many scientist believed that even very subtle changes in the chemistry of DNA would be disastrous. This discovery is the first of its kind, and opens up the possibility that life can thrive in a much wider variety of conditions than previously believed. Therefore, it may not be as much a question of what kinds of environments life can adapt to, but more simply what kinds of environments life has the opportunity to evolve in. It could be that, given enough time and a gradual enough transition, life can adapt to nearly any environment.
http://news.nationalgeographic.com/news/2010/12/101202-nasa-announcement-arsenic-life-mono-lake-science-space/
http://www.guardian.co.uk/science/2010/dec/02/nasa-bacteria-arsenic-phosphorus
