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Life, But Not As We Know It

The import of the discovery of a new arsenic-based microbe is that finding life as weknow it will give us a better shot at testing for biology on worlds that are, both by definition and in fact, truly alien.
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"Arsenic and Old Lakes" is what Laurance Doyle, one of my colleagues at the SETI Institute, called NASA's much ballyhooed press conference last week.

It turned out that the subject of the new research was a microbe, colorfully named GFAJ-1, that can incorporate arsenic into its body chemistry. Interesting news, but not everyone felt that the story justified NASA's pre-release publicity, which suggested that the new research was a major milepost in the search for alien life.

Indeed, many thought that the agency's advance notice had wandered beyond the misty borders of "tantalizing" into the dangerous land of "hype." On the day before the press conference, my in-box bulged with dozens of inquiries about the upcoming revelations, asking whether NASA was about to tell us they had finally found proof of extraterrestrials. After all, if the research to be disclosed at the press event was not at least this dramatic, then why was the publicity overture so seductively coy?

When the news turned out to be about a terrestrial organism, many denizens of blog-land felt duped, and began to turn on the research itself. They questioned why NASA (which, as they helpfully noted, has the word "space" in its name) was shelling out taxpayer dough to examine pond scum in a California lake? And why was such a thoroughly earthly endeavor classified as "astrobiology" -- a discipline that sounds like the day job of the Enterprise's Science Officer?

But let's back up a minute. There's no doubt that the work by Felicia Wolfe-Simon is exceedingly cool. After all, it shatters another of those rules of nature that sounded good in high school, but turned out to be untrue (e.g., "matter can neither be created nor destroyed" or "all life falls into two kingdoms; plants and animals.") In this case, the sundered wisdom was that biology -- all biology -- is largely built of only six elements: carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur (CHNOPS). This idea has been considered such a basic fundament of life, it was even part of the Arecibo radio message that was famously beamed into space three dozen years ago. There weren't a lot of things we could tell the aliens in that cramped transmission, but CHNOPS was one of them. (Actually, the sulfur was not mentioned, as it's not part of DNA.)

So from a biological perspective, the fact that these microbes could select arsenic, rather than conventional phosphorous, from the environmental menu is remarkable. If GFAJ-1 has actually incorporated arsenic into its DNA, then it has morphed -- at least temporarily -- into a different kind of biology.

Sci-fi has long entertained the idea of life-but-not-as-we-know-it. Mostly, it favors silicon-based life -- as much a staple of space opera as bulbous eyeballs. And silicon-based life makes at least some sense, since the element lies immediately beneath carbon in the periodic table. Consequently, its chemical deportment is closer to carbon than any other element.

Well, arsenic lies just below phosphorous in the table (indeed, its chemical similarity is -- at root -- the cause of its utility for chilling enemies of the Borgia family in renaissance Italy, not to mention obnoxious in-laws in the Victorian era.) But while sci-fi writers picked up on silicon, they don't seem to have proposed arsenic-based extraterrestrials.

And while it's true that the microbe studied by Wolfe-Simon and her colleagues, despite being able to use arsenic, still preferred phosphorous, the result is nonetheless remarkable. Indeed, it's akin to the joke about the talking dog: the surprise is not that it can do it well, but that it can do it at all.

The bottom line, and the reason why this work is both relevant and encouraging for the search for cosmic company is this: In our efforts to find extraterrestrial life, we can easily run into a confounding problem -- recognizing life when we see it. Of course, there won't be any difficulty knowing that we've found life if it's of the hairless, humorless Klingon variety. But it's safe to assume that the overwhelming majority of alien creatures will be microbes.

And frankly, recognizing a speck-sized species on another world is problematic. In 1976, NASA sent a very expensive and sophisticated pair of landers to the rusty, dusty surface of Mars. These robot biologists conducted several experiments to ascertain whether the martian soil might be laced with metabolizing life. But even today, the results are disputed -- and that's at least partially due to the fact that the landers were looking for life as we know it.

So forget the hype. The import of this story is that finding life as we don't know it in a California lake will give us a better shot at testing for biology on worlds that are, both by definition and in fact, truly alien.

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