Of Arsenic, Slime Molds, and Life on Other Worlds

by Jennifer Frazer on December 9, 2010

I have kept silent on last week’s announced discovery of bacteria from Mono Lake, California, alleged to be able to grow using arsenic instead of phosphorus — until now. I was reading a news analysis on the subject of the improved odds for life given this and other recent discoveries in biology and astronomy in my morning paper and stumbled on this intriguing allegation:

Another reason not to get too excited is that the search for life starts small – microscopically small – and then looks to evolution for more. The first signs of life elsewhere are more likely to be closer to slime mold than to ET. It can evolve from there.

I’m not sure whether to take that as in insult to an incredibly evolved and highly complex life form or not. Hey — how many protists do *you* know that can learn to anticipate regularly timed stimuli, drive robots, solve mazes, and plan high-speed rail routes? Nonetheless, I do get his point — that if we do find life, it’s not likely to have made it much past the basics of cell, membrane, and genetic code. Which got me thinking about something that’s bothered me for a while.

I have been to Mono Lake (pronounced “moe’-noe”), and it is truly an unearthly place. I can see why one might search there for  — as they put it on Wait, Wait Don’t Tell Me this week — yet another alternative lifestyle in California. I know the basics of the chemistry involved, but I don’t know enough to know — as has been claimed by several critics — whether what the scientists have found is highly dubious. According to Carl Zimmer’s roster of experts, it’s all but impossible the authors of this paper performed good science with valid conclusions, although it’s not impossible arsenic-based life exists. (Aside: One of the authors, Felisa Wolfe-Simon, named the bacterial strain GFAJ-1 for “Give Felisa a Job”. Although I normally 100% support such creative naming efforts (scientists are usually dull as dirt when it comes to naming things, and why not name things creatively? One classic example: a development gene named hedgehog inspired the name of a related gene: “sonic hedgehog“), in light of recent events, Felisa’s probably regretting that now.)

But here’s what bothers me about the leap people make whenever they find bacteria that can eat arsenic or live in boiling acid or leap tall buildings in a single bound: that finding extreme life here on Earth makes finding it on other planets more likely. I’m not an astrobiologist, but claims of this sort have always irritated me. They make similar claims because we find life in all sorts of high-wire places on Earth: miles beneath the surface in microscopic rock crevices and pores, in freezing Antarctica, in salt flats, in hot springs, and in barren wastelands of all sorts that support nothing else.

But to me, that misses the point. As far as we know, Earth has, almost from the beginning, hosted a warm, cushy, UV-shielding, stable-chemistry-and-solvent-providing ocean. Almost from the beginning. Granted, the Late Heavy Bombardment could have boiled the oceans away temporarily, but that was a blip. Our atmosphere has gone through at least two great gas revolutions, and the land, initially unprotected by a thick atmosphere or an ozone layer, was a UV-scorched, life-shriveling place. But deep beneath the waves there was always a place of refuge for life to start, to begin, to evolve. In other words, Earth had a cradle where life could begin in relative safety and consistency.

After life evolved in this watery nursery, in which there was no time pressure and plenty of space to work out the basics, gain strength and, one might even say, genetic confidence, it had plenty of additional time — billions of years — to branch out, explore, and master the extreme environments of Earth. Bacteria and archaea may have even been forced into those extreme niches because of competition for the easy life elsewhere.

But what about planets with extreme chemistry or biology that never had a safe ocean; or, had an ocean, but, probably like Mars, had one only fleetingly? Would life have found it easy to begin or have time to take hold in such a forbidding place? Some planets and moons host methane oceans, and Europa may have its own water ocean beneath its icy crust. In those places I might be convinced life could evolve. And there are some life-origin theories that do not require oceans.

But personally, I put my money on the sea. And for the vast majority of places, evidence of extreme microbes on Earth — whether they bathe in acid baths or can get by on arsenic — will not convince me that life in places that have only ever known such conditions is likely*.

What do you think?


* And I still wish the other bizarro over-the-top microbial life we have on Earth could get half the attention that one little otherwise-relatively-garden-variety bacterium that might be able to survive on a phosphate-free diet gets.

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Daniel December 9, 2010 at 10:50 am

Amen sister! Hope and optimism are great traits for a scientist to have, but wild and ungrounded speculation is generally not. For full disclosure, I’m not a scientist, but I believe that there’s enough Wow! to be gained from incremental scientific advancement (not to mention the stuff we’ve already learned) that we don’t need to go inventing alien landscapes without reason. I’ve faith that there’s life out there, but if and when we ever find it, it’ll be one step at a time.

All that being said, I’ve always loved that Star Trek had the Horta. Boo to the “all-aliens-must-be-carbon-based-hominids” attitude! :-)

Christian Drake December 9, 2010 at 1:20 pm

As a lover of wild and ungrounded speculation, and one who chimed in perhaps too early on the GFAJ-1, before the current controversy, AND as someone who has loudly espoused the opinion that extremophile microbes on Earth suggest a greater chance of extraterrestrial life (on Friday, for one instance), I have a few comments.

I get what you’re saying. It makes sense. We on Earth have it easy, and stability is indeed the key to evolution. But do I agree that all life MUST have an ocean nursery in which to begin? No way. I only imagine that our oxygen-rich, watery planet hasn’t fostered the only life out there, just the best. Because we had easy beginnings, life could evolve to its present state where millions of species form an intricate network of ecosystems, and where such beings as dinosaurs, humans, and roasted chickens could evolve. If there’s methane-based life on Titan, I doubt it would ever get beyond the microbial stage. But that certainly doesn’t mean it can’t start.

dinahmow December 9, 2010 at 4:37 pm

Well, I passed Fourth Form chemistry, but that’s as far as I went! Even so, I struggle to believe that something that might begin in methane or arsenic could evolve much beyond its beginnings.
I am one of “oceans-are-nurseries” people. And places that never had or no longer have oceans? That’s a mighty long bow to draw!

Jennifer Frazer December 9, 2010 at 11:11 pm

Christian — You have an apt last name for discussing this subject! (for those of you wondering why, see here). I see what you’re saying too. And you’re right — it’s possible. Nothing is impossible, and thank goodness for that! : )

Although I do sometimes wonder about methane-based life. Many fundamental properties of our cells are made possible by water’s polar, hydrophilic (duh) nature. For instance, membrane lipids agglomerate as they do because they have hydrophobic tails and hydrophilic heads. How would that work with hydrophobic methane as a solvent? Would their membrane lipids (if they have such) simply be turned inside out? If they use DNA, how would handling that differ given that it’s strongly negatively charged? Interesting to ponder.

kati December 9, 2010 at 11:48 pm

first of all, i agree with you that more of our world’s own fantastic creatures should get more interest than they do and/or compared to the interest in extraterrestrial life.

but maybe i’m naive (and not a qualified scientist – although i’ve always considered myself to be a scientist at heart) but it seems sort of limiting and pessimistic to sound so sure of the confines of Life. i think about all the things we know today compared to two hundred years ago. what will we discover in the next two hundred? our planet is proof that Life is determined and scrappy and adaptable and i can only imagine that it is the same way elsewhere. in ways that we can’t even fathom until we find it. i have a hard time saying “our oxygen-rich, watery planet hasn’t fostered the only life out there, just the best” and “If there’s methane-based life on Titan, I doubt it would ever get beyond the microbial stage”. but maybe i’m just a dreamer :)

Molly Malone December 10, 2010 at 4:08 pm

I was watching the NASA conference live and at the very start of the interview, I began to think that it was more of a political spotlight grab than an actual science discovery. I think the Guardian’s “Lay Scientist,” Martin Robbins, put it best:

“What’s much more interesting is that the drama has given us an opportunity to see how a collection of related problems in different areas of science outreach can combine to seriously damage the credibility of a highly-respected scientific institution, and by extension science itself. ”

It’s too bad they jumped the gun, released a possibly false statement about having found something of relevance to extra-terrestrial life (I mean, c’mon, isn’t all life on our planet in that category? If we can evolve, others can evolve.) I agree that the odds are in favor of life coming from an ocean, but there’s too much weirdness out there in the universe to say everything would evolve that way. I just think the odds are highly in favor of it happening that way, but there’s always a miniscule chance that something immensely out of the ordinary could happen. I think of it like the Heart of Gold analogy from Hitchhiker’s Guide to the Galaxy. The odds of finding a sperm whale and bowl of petunias appearing out of nowhere is statistically irrelevant. But who knows? Maybe it’s possible.
The point is it’s not likely, and NASA should really be focusing on the stuff which has a reasonable possibility of happening- or, of being detected, rather than speculating on the possibility of whales appearing in thin air or bowls of petunias. The whole news conference was an intriguing “what if” which was better left to private speculation and further research. This whole thing has marginalized the credibility and importance of NASA still further.

Christian Drake December 10, 2010 at 6:12 pm

Jennifer: Ha ha, yeah, no relation to Frank Drake, but I’ve been obsessed with the Drake Equation for years, in part due to narcissism, no doubt. But mainly my glancing interest in astrobiology has something to do with my love of science fiction: As the best sci-fi acts as a mirror to reflect the ethics of today’s society, so the search for extraterrestrial life puts Earthbound life in perspective. It’s a bit like Carl Sagan’s “Pale Blue Dot” photographic essay puts the planet in perspective. We can learn about the universe from the workings of the Earth as much as we can learn about the Earth by studying the mechanics of the universe. If NASA’s latest finding prove to be on point, despite new evidence to the contrary, it would make true the reverse of the old saying, “on Earth as it is in Heaven.”

Kati: I’m a dreamer, too. Statistically speaking, it’s highly improbable that we’re the only intelligence in the universe. But it’s also probable that if there are intelligent races out there, they’re made of the same stuff as us; analogues of phosphorus and carbon, like arsenic and silicon, simply don’t share the properties that make complex life forms possible. But finding even microbes on another world would be a huge coup for humanity’s understanding of itself and our world.

Alan December 13, 2010 at 1:52 am

When I hear the doubts about life being possible elsewhere, or that methane based forms would not be able to progress past the microbial stage, I have to reset the argument.

Were a lifeform to develop in methane, or arsenic, or what have you, it would likely bear little or no resemblance to microbes. To assume that it would is to assume that it is DNA based. As a computer programmer, I look at this as a million monkeys at typewriters sort of situation. You can’t assume that self replication can only take one track, that DNA is even required, or that it must be based on hydrogen and oxygen. All you can assume is that it must be capable of self-replication, have an abundant energy source on which to thrive, and an environment that would not be fatal. I don’t think you can assume that life needs a warm creche to develop in before it ventures out to hostile environments. Beyond that it’s random (or directed) events that get you to life.

I find both the ideas – that EBEs must be way ahead of us, or must be way behind us amusing. There’s no reason to assume that we are the measuring standard for the universe. We may be the latest, or the first. There may be nothing but potential out there. Or there may be thriving ecosystems out there that we haven’t discovered. There may be others that we’ve passed over because we didn’t even understand what we were looking at. It’s not like that hasn’t happened before.

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