NASA published a short and cryptic press release on 29 November: they commented that they were arranging a news conference for 2 December “to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life.” The obviously intended effect occurred pretty much immediately: the media and internet were set buzzing with widespread speculation as to what exactly this could mean, ranging from the prosaic to the preposterous.

It turns out it was much more prosaic than even many more circumspect commentators had speculated: they discovered evidence that a bacterial strain found on Earth was capable of metabolizing arsenic (As) and incorporating it into structural molecules of the cell. Researchers found a strain of gamma proteobacteria known as GFAJ-1, found at Mono Lake in California, can feed on As and incorporate it into its biological structures when there was a shortage of phosphorus (P)….

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