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Alien arsenic eating bacteria redefines life?

On November 29, NASA released a tantalizing message for the media, stating that they will "hold a news conference at 2 p.m. ET on Thursday, December 2, to discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life." This set off a round of speculation, and when the embargo lifted on the actual Science paper, several news articles hyped up the actual findings. There were headlines connecting the discovery of alien life to bacteria that can survive in arsenic and claims that the discovery "redefines life as we know it."  Thankfully, there are news sites that fought against the hype to produce fair and balanced analyses.

The actual scientific findings are exciting enough on their own.  A strain of bacterium dubbed GFAJ-1 can grow in a medium abundant in arsenic and scarce in phosphorus. There is also evidence that the bacteria can substitute phosphorus with arsenic in the backbone of DNA and possibly other biomolecules. This discovery does indeed have an impact on astrobiology and evolutionary chemistry, as it's another example of how flexible and resilient life can be. However, we should also regard the results critically.

These bacteria by far prefer phosphorus over arsenic. Even when grown in a medium that only contained trace amounts of phosphorus, they still incorporated it into DNA, choosing arsenic seemingly as a last resort. Furthermore, the bacteria are certainly not a new life form. They originate from the arsenic rich environment of Mono Lake in California.

Several sources also announced that this discovery will drastically change the search for alien life, which is untrue. The search for life is not based on specific elements, but rather on possible building blocks for life. While the new finding definitely demonstrates that life can be strange and wondrous, it's important to avoid overexcitement. Hype will only serve to confuse and further complicate the communication between the science community and the general public.

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