The arsenic aliens that aren’t

Paul Raven @ 03-12-2010

Typical, really; the day I’m away from my desk, a big sf-flavoured story hits the blogosphere. I speak, of course, of NASA’s press conference about the discovery of “alien” life… not at the top of the gravity well, but at the bottom of an arsenic-laced lake in Yosemite National Park. From Wired UK (whose new page layouts are much easier on the eye, but disappointingly similar to their US counterparts):

The bacteria, found in the bed of Mono Lake, are believed to exist as a second form of life — using arsenic in cells in place of the phosphorous found in most living cells.

That suggests that they’ve developed entirely independently from our life, implying that if life has evolved twice on Earth, then it’s far more likely to have evolved off Earth too — especially as it’s believed by astronomers that among stars similar to the Sun, as many as one in four could have small rocky planets like Earth, at least some of which would occupy the same “goldilocks zone” that Earth exists in — neither too hot, nor too cold, for life to emerge.

Leaving aside the actual story for a moment, the meta-story – namely how excited the public can get about the possible announcement of alien life – is worth considering as well. I’ve got no criticism for NASA over the way they framed their announcement; it’s no more duplicitous than the PR operations of the average corporation or government, and I know which I’d rather be paying attention to. But as New Scientist points out, the possibility of actual evidence for extraterrestrial life – which is what a lot of people thought (or hoped) was on the cards – was embraced with a cheery enthusiasm by all sorts of news outlets. Perhaps the world’s gotten so weird lately that nothing can surprise us any more… or perhaps we’re still secretly hoping that sentient ET(s) will turn up, Intervention-style, and pull our collective homo sapiens backsides out of the frying pan we’ve been cheerfully heating up for ourselves. (The writer – and reader! – in me would still quite like the latter to happen, not because I think we actually deserve a species-level bailout, but because the frying pan would doubtless be succeeded by a very interesting succession of fires.)

Anyway, the important thing about the arsenic-alien-life story is that it’s not quite as big a deal as the headlines would have it. It’s still pretty fascinating stuff that connects to extremophile life, but – as explained by Paul Gilster at Centauri Dreams – it’s not evidence for “shadow biospheres”, and doesn’t really tell us anything about extraterrestrial life that we haven’t already hypothesised.

Let’s leave the astrobiology aside for the moment and simply focus on the fact that life is fantastically adaptable in terms of biochemistry, and can pull off surprises at every turn. That’s always a result worth trumpeting, even if it leaves the wilder press speculations in the dust. After all, it’s long been assumed that the six elements that underlay the basic chemistry of life are carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Despite persistent speculation, few thought life could exist without them.

[…]

Can these bacteria replace phosphate with arsenic naturally? Wolfe-Simon herself says thirty years of work remain to figure out exactly what’s going on, a comment on the preliminary nature of this work, which remains controversial in some quarters and is in obvious need of extensive follow-up. No shadow biosphere yet, but obviously the quest is ongoing because of its implications, and we’ve now received one very tantalizing piece of evidence that such things may be possible.

If life really did start here more than once — a finding that is not remotely demonstrated by this work — then we can talk about how likely it will have done the same thing on distant planets, upping the chances that we live in a universe where life emerges whenever given the chance.

And here’s PZ Myers, taking a break from being Dawkins’ bulldog to dig into the actual science of the paper:

You’d predict just from looking at the [periodic] table that arsenic ought to have some chemical similarities to phosphorus, and you’d be right. Arsenic can substitute for phosphorus in many chemical reactions.

This is, in fact, one of the reasons arsenic is toxic. It’s similar, but not identical, to phosphorus, and can take its place in chemical reactions fundamental to life, for instance in the glycolytic pathway of basic metabolism. That it’s not identical, though, means that it actually gums up the process and brings it to a halt, blocking respiration and killing the cell by starving it of ATP.

Got it? Arsenic already participates in earthly chemistry, badly. It’s just off enough from phosphorus to bollix up the biology, so it’s generally bad for us to have it around.

[…]

So what does it all mean? It means that researchers have found that some earthly bacteria that live in literally poisonous environments are adapted to find the presence of arsenic dramatically less lethal, and that they can even incorporate arsenic into their routine, familiar chemistry.

It doesn’t say a lot about evolutionary history, I’m afraid. These are derived forms of bacteria that are adapting to artificially stringent environmental conditions, and they were found in a geologically young lake — so no, this is not the bacterium primeval. This lake also happens to be on Earth, not Saturn, although maybe being in California gives them extra weirdness points, so I don’t know that it can even say much about extraterrestrial life. It does say that life can survive in a surprisingly broad range of conditions, but we already knew that.

I can’t help but feel a twinge of disappointment myself, really; cynical I may be (YA RLY) but I’d still love to hear we’d found solid evidence of truly alien life. But you know what? News that the life we already know works in weirder and more tenacious ways than we previously thought is enough to give me a sensawunda kick. I suspect that if you’re not continually astonished by nature’s diversity, you probably don’t yet know enough about it*.

[ * Yeah, I’ve been binging on documentaries from the BBC’s iPlayer service on these chilly evenings; so sue me. I might as well enjoy bachelordom to the full, no? 😉 ]

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3 Responses to “The arsenic aliens that aren’t”

  1. Nancy Jane Moore says:

    It was interesting news, but not all that surprising. Ever since I found out that some bacteria can thrive on the inside of a nuclear reactor (unlike most of life on Earth, they like radiation), I’ve figured the urge to life is such a strong force that it will crop up in all kinds of unexpected places. I have no doubt there’s other life out there and I will not be surprised if it isn’t carbon-based, either. I just hope someone finds real evidence of it before I kick off this mortal coil.

  2. Jeb says:

    Well, if you remember that their blood is made of acid, and that people chops is their favorite food, then everything will be cool. Actually, I prefer the ET style of alien because we share a love of reases pieces (sp?)

  3. Buffalo says:

    The story is sort of a romantic sci-fi kind of puff piece, isn’t it? Though it is good to know that we can still be surprised by things and that science hasn’t figured out everything… quite yet. I do wonder a bit about this whole quest for extraterrestrial life. What’s the real reason when our planet is teeming with life already and we don’t seem to think that is very remarkable at all? Is it just because of the novelty factor? I bet within a few weeks of discovering some extra-terrestrial life form, the news would forget it completely and be back looking at the stock markets and international wars, etc. It’s sad really.