Most of life -- down to its protein, fat and DNA -- is made from just six chemical elements: carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus. In the California experiment, the researchers said arsenic compounds effectively took the place of the phosphorus in the bacteria.
"The idea of alternative biochemistries for life is common in science fiction," said Carl Pilcher, director of NASA's Astrobiology Institute in Moffett Field, Calif. "Until now a life form using arsenic as a building block was only theoretical, but now we know such life exists in Mono Lake."
If that can happen, what else is possible? Could there be places in the universe where silicon does what carbon does on Earth? Where other combinations happen that haven't occurred to earthly researchers, looking for life that resembles ours?
"We still don't know everything there is to know about what makes a habitable environment on another planet," said NASA's Pamela Conrad, who is on the team that built Mars Science Laboratory, the next probe scheduled to land on the red planet in 2012. "We have to increasingly broaden our perspective."
Some scientists were skeptical. Steven Benner of the Foundation for Applied Molecular Evolution called the finding "an exceptional result" -- but said that was precisely the problem with it: GFAJ-1 may just be a fluke. Compounds containing arsenic would probably fall apart more easily than those with phosphorus.
Other scientists later criticized the paper, saying the team had not proved the bacterium was actually using arsenic compounds in place of phosphorus. See more HERE.
Still, today's report could be big, said Keith Cowing, who runs the website NASA Watch. "It shows that other biochemistries are possible, more than just 'life as we know it' and that the possible places where 'life' could exist in the universe are now much more numerous as a result."
"We've cracked open the door to what's possible for life elsewhere in the universe," said Wolfe-Simon, the lead researcher. "And that's profound."