Wow! It turns out that phosphorous is not necessary for life... bacteria can survive just fine on arsenic!
"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."
http://www.nytimes.com/2010/12/03/science/03arsenic.html?src=me
"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."
http://www.nytimes.com/2010/12/03/science/03arsenic.html?src=me

