The controversial claim of microbes that exhibit arsenic rather than phosphorus in their biochemistry has been retracted by the journal Science 15 years after it was first published — but while most in the research community are pleased by the decision, the retraction has angered the authors of the original study.
Arsenic, as we know from its use as a poison, is a toxic substance. Thus, life as we know it of course would not include arsenic in its biochemistry. Yet, because the search for alien life is, by its very definition, a search for life as we don't know it, astrobiologists like to consider the possibility of organisms that have a different biochemistry to the one we're familiar with.
