The Big " 'Scuse me!" on Mars

People rarely like to talk openly about flatulence--it's a topic that, one might say, just doesn't smell right.  But it's a normal digestive function, a release from what otherwise might do a person or animal in.  So when it makes the headlines, we as responsible bloggers can't just ignore it.

What we refer to, of course, is the Big Fart that NASA is now reporting to have discovered on Mars; the identification of methane bursts, as described by Webster et al. in the Dec 16 issue of Science, as well as all over the popular media, including here at the NYTimes.  NASA says methane can only be present for two reasons.  Kenneth Chang in the NYT writes "It could have been created by a geological process known as serpentinization, which requires both heat and liquid water. Or it could be a product of life in the form of ancient microbes known as methanogens, which release methane as a waste product." We can joke about some buried, covey of hibernating Green Giants (or Green Sheep) dormant underground, cowering in shelter from the harsh surface condition, but expelling from time to time.  This would overstate what is being suggested, sure, but it points to some important issues.  So, with our usual level of skepticism, we can try to outline what we see are some of them.

Public domain image of Mars, 1980.

The hint or even suggestion of course is that a burst of methane may signal not just that life used to be on Mars, but that life is still there, hidden under the surface (is it a hypothesis of last resort, since there isn't any on the surface?).  An important point is that methane doesn't last very long before degrading.

What is Life?

There are, however, some tiny details that are worth discussing.  Why do we assume that 'life' means organisms of complex nature using Earth-like metabolism and presumably based on DNA and RNA or its equivalent?  That is, why should  life on Mars be the same as life on Earth?  Are 'microbes' like ours inevitable if there is life?

There are many arguments over what life 'is'.  If one thinks of it in terms of self-reinforcing proliferation via chemical capture of solar energy by partially isolated subunits, like cells or other structures, then it is said that only carbon or silicon could be the basis of it.  That's different from, say, mere crystal growth.  Chemists have also shown the fundamental physical reasons why lipid layers form and how the ATP-based processing of energy works and is fundamental to life here on Earth.  Some believe that this is the only way such things might happen.  There are also diverse, and disputed, ideas about where the first life on Earth, the primordial 'soup', was--perhaps in undersea hot geothermal vents and so on. Again, we can't pass judgment on that.  Indeed, some seem to have argued that RNA and DNA will inevitably be the basis, and the means, of the evolution of life, no matter where it occurs.

But this is all derived from what we know about life on Earth.  Why does it have to be the same on Mars?  And, if methane is an indication of life, to complicate things further, there is also the issue that, since there appear to be no multi-celled organisms on Mars, methane there would have to be the result of bacteria digesting other complex material produced by life.  That is, the microbes have to be eating the result of some other DNA-based life.  If not some other, higher forms of life, are the methanogens digesting their dead ancestors or is, or was there other complex life's detritus to eat?  

Assuming that's what's going on, one can then construct scenarios by which natural selection would lead to cellular organisms on Mars (such as found around 3.5 billion years ago on earth), even if there aren't any subterranean gaseous little green Martian sheep.  If such microbes were truly there, it would be a genuinely interesting finding and something NASA could not be criticized for reporting, nor the NYTimes or Science criticized for highlighting. But these are large assumptions. 

And indeed, as we noted above, there are apparently other ways that methane can be made or found on Mars--NASA itself points this out--and a large part of the December story about methane has to do with controversial previous reports that were apparently artifacts, which authors of this new report are saying they hereby resolve. So, the major purpose of this new flurry of news!! about methane on Mars is to establish the fact that there really is methane on Mars.   

But NASA and news outlets aren't ignoring the possible implications about life, so let's suspend all skepticism and ask whether this scenario could have any other implications.

What if it's true?
The idea would be that the same sort of evolution that has occurred on Earth also occurred on Mars.  It would have originated some half-billion or so years after Mars basically formed, and  DNA/RNA-based microbial life would have evolved, with the same sort of biochemistry as life on Earth, involving the release of methane.  Or was it underground Martian men, or methane-releasing cows....or even green?  But why would they be what the word 'microbe' tends to suggest--earth-like biological species?  Is it because simply that without any better imagination, one reasons that if there's methane there must be life--and that means life as we know it?

Mars’ origin was probably at a time not that different from the Earth’s, given the estimated age of the Sun (5 billion years).  But the Martian surface has been essentially dead, too cold and with atmospheric pressure too low to allow liquid water at least for the last 3.8 billion years (data from Wikipedia).  That means that the methane belchers either evolved way long ago and died out, leaving methane pockets to leak out still to this day (though methane degrades quickly, according to the news reports, as in within a few hundred years), or they somehow evolved the ability to live beneath the unlivable surface, and to move around (so as to evolve), for millions of years.

Further, as we noted above it amounts to assuming that Earth-like life is what was evolving there, with Earth-like metabolism.  But this evolution was either over and done with long ago—and hence occurred very much faster there than here, or has to be imagined as going on subterraneanly for that long—needing of course some source of energy other than sunlight (and hence something other than photosynthesis or perhaps even ATP-based storage), and probably needing liquid water.  And if still flatulent, how did the methane persist?

Methane on earth is produced by micro-organisms using the complex multi-part protein methyl-coenzyme M reductase (MCR), but of course this also involves chromosomes, DNA coding, DNA regulation, and RNA directly and even indirectly (e.g., those many genes involved in energy capture, nutrient capture, replication, protein processing, and much besides). It's fair to ask how likely, or even plausible, it could be that the same sort of reaction system would have evolved twice, or what the basis is for giving priority explanatory credence to saying that it is far more likely to be due to something else. 

But since, to us anyway, the odds seem very heavily stacked against independent origins, this would then raise the possibility that life originated elsewhere than here on Earth, either on Mars or somewhere else, and was seeded here or there, or both, from space. Many (including Francis Crick) have tried to make that case, and we know that molecules that life uses exist in space and have rained down on Earth (and presumably also on Mars). But there is no evidence that this rain is of other than very primitive molecules and nothing at all organized like real life. That is, no space probe or meteor or its like (or landing on a comet) have found DNA, RNA, complex proteins, or microbes.

Based on a great consistency among methods of analysis, all present life on Earth seems to have descended from a common beginning.  Of course that could have been seeded, even from Mars via meteors or whatever, but only one such seed ‘took’, it happened well over 3.5 billion years ago, and when and where it dropped, the Earth had to have been geochemically and environmentally ready for it, which means that whatever led to its evolution on Mars or elsewhere, conditions were similar enough here compared to its source, for the drop-ins to survive and evolve.  Or, the transport could have been from Earth to Mars, except that by the time bacteria evolved here Mars seems to have already become uninhabitable, even for microbes. 

If ready-made microbes rained down here, their forms would all have had to have evolved somewhere else with essentially similar conditions as here, and the microbes would have had to withstand the rigors (including mutagenic cosmic radiation) of light-years of deep space travel to get here.  And must then have found essentially immediate ways to live and replicate, wherever and whenever it was they landed, before dying due to conditions inimical to their needs.  And if from some other planet, then why does all life seem by various criteria to have originated here at 3.5 billion years?  Yes, after the fact we can construct all sorts of contorted explanations, but it's a post hoc stretch.  Quite a stretch.

Or, is it plausible to assume methane as a sign of life if we have to say as well that with an entirely unrelated path, not protein or DNA dependent, say, evolved at the same time (and underground) on Mars ending up as methane producers?  Why such exquisite parallelism?

While of course, we cannot rule any of this out (and chemists and geologists are now earnestly considering other methanogenic mechanisms that would explain the Martian finding), there is a massive burden of implausibility that reporters should be requiring NASA et al. to overcome before repeating the kinds of excited tales we’re seeing blazoned across the headlines.  The reporters may not have thought of the above sorts of issues, but the scientists have, or should have.  And it's reporters' duty to know of these sorts of things or else not write about them!  

The implication that very similar RNA/DNA/protein based life evolved in remarkably similar or even eerily coincidental ways, on Mars, or anywhere else with transport potential to Earth is a leap of credence of dramatic proportions, unless of course it’s just wishful thinking and the usual publicity stunt aimed at funders.

If the carefully caveated suggestions of life on Mars were to turn out to be true, then everyone will agree that it will be remarkable in unprecedented ways, and as fascinating as the evolution of life itself, here or anywhere.  The best discovery since ice cream, for sure.  But from what is being reported, there are far too many reasons to doubt the claims that a little runabout, on a trivial part of Mars’ surface, detected a bathroom odor from subterranean beasts.  Because the  proclamations just don't smell right.