The Washington Post today has an exceptionally clear report on Felisa Wolfe-Simon’s claim that she may have found arsenic based life at Mono Lake in California. Here’s how the Post piece opens:
All life on Earth – from microbes to elephants and us – requires the element phosphorus as one of its six components. But now researchers have discovered a bacterium that appears to have replaced that life-enabling phosphorus with its toxic cousin arsenic, raising new and provocative questions about the origins and nature of life. News of the discovery caused a scientific commotion this week, including calls to NASA from the White House asking whether a second line of earthly life has been found.
And here’s how the Post characterizes the experiment that Felisa Wolfe-Simon did:
The bugs she worked with, an otherwise common bacteria in the halomonadaceae family, thrived without phosphates and with lots of arsenic. She then used cutting-edge instruments to determine that the arsenic was embedded in the core genetic and energy-transfer systems of the bacteria – that it appeared to have replaced (or preceded) the phosphorus. . . . She said that while small amounts of the phosphorus remained in the arsenic-based bugs, she was able to determine that it was definitely not enough to supply the presumed phosphorus needs of the cell. That, she said, was being done with the arsenic. “Sometimes I’m asked why something like this has never been found before, and the answer is that nobody has run the experiment before,” Wolfe-Simon said. “There was nothing really complicated about it – I asked a simple question that was testable and got an answer.”
Ask nature a question; get an answer. That’s science, and that’s what Felisa Wolfe-Simon did.
Paul Davies is quoted in the article as saying that what Felisa Wolfe-Simon has discovered is “the tip of a huge iceberg,” clearly implying that he thinks a shadow biosphere exists on earth. But the Post also quotes another scientist, Steven Benner, as being less convinced:
Chemist Steven Benner of the Foundation for Applied Molecular Evolution in Florida has been involved in shadow biosphere research for several years, and spoke at the NASA unveiling of Wolfe-Simon’s work. He says that the Mono Lake results are intriguing – “I do not see any simple explanation for the reported results that is broadly consistent with other information well known to chemistry” – but he says they are not yet proved. A primary reason is that arsenic compounds break down quickly in water while phosphorus compounds do not. His conclusion: “It remains to be established that this bacterium uses arsenate as a replacement for phosphate in its DNA or in any other biomolecule.” The tests to make a more final determination, he said, are complex but available.
So those additional tests will have to be made before drawing too many conclusions about these microbes. Our current background knowledge of what’s possible chemically is certainly being challenged by Felisa Wolfe-Simon’s interpretation of what she thinks she has found. And wherever existing background knowledge is being upended by what appears to be a strong claim, it’s time to apply serious scrutiny to the claim itself (as well as refreshed scrutiny of our background knowledge). This heightened scrutiny needs to be applied both ways for the sake of coherence. You can’t treat new claims as true, or as knowledge, when they contradict everything else that you think you know about the world. Here’s another quote from the Post article:
“This is different from anything we’ve seen before,” said Mary Voytek, senior scientist for NASA’s program in astrobiology, the arm of the agency involved specifically in the search for life beyond Earth and for how life began here. “These bugs haven’t just replaced one useful element with another; they have the arsenic in the basic building blocks of their makeup,” she said. “We don’t know if the arsenic replaced phosphorus or if it was there from the very beginning – in which case it would strongly suggest the existence of a shadow biosphere.”
Extraordinary claims require extraordinary evidence, and Felisa Wolfe-Simon is asking her colleagues to consider a very, very extraordinary claim. Here’s how she puts it:
If something here on Earth can do something so unexpected – that breaks the unity of biochemistry – what else can life do that we haven’t seen yet?
Breaking the unity of biochemistry is a pretty big deal. That’s why, as this news story evolves, the “if” in her question has to remain firmly in play.