Monday, September 23, 2013

Does Mars--or can Mars--tell us much about the origin of life?

The latest hot item from NASA is the statement (is it an admission?) that there's no methane, and thus no trace of E. coli on Mars after all.  Well, they never hinted it would actually be E. coli, but at least some kind of bacteria (or 'microbe').  Now, after a year of exploration, apparently the rover has come up as empty of evidence as the Martian canals are of water (and maybe with old wrecks of gondolas).

Actually, for a few microseconds there was some advertised reason to think that the Red Planet was the birthplace of microbes: SARS from Mars, if you will. Some geologic formations in meteors found in Antarctica and apparently from Mars, were touted as essentially fossilized microbe remains.  It was quickly shown by sober scientists that these were natural geological or mineral formations, with no real evidence of actual life, but some clung to the hope (or was it hype?) that the bug-like formations really were bacterial coffins.

Still, hope forever in the human heart, so to convince us we should pay for missions to Mars rather than Mars bars to missions (to feed hungry people), the continual drumbeat from NASA has been the search for life.  In more tempered terms, even the scientists involved have been warning that the signatures of past life (nobody thinks Mars still has living wigglies, to our knowledge), will be very indirect.  Signatures of molecules related to life as we know it here on Earth.  In this case, Curiosity was seeking traces of methane (bacterial flatulence), but in vain.  Even the enthusiastic but responsible investigators noted that there are other ways for molecules such as earthly life uses  to get to Mars, such as bombardment from space, for one.  We'll return to this later.

Instead of a thrilling Nature cover story, Mars is as dusty and devoid as a pancake on a griddle:

From the BBC online story of Sept 19, 2013

What a crushing blow!  Think of the billions of dollars lost to Hollywood alone, by depriving them of countless movies about the past (or evil subterranean present) on Redsville.  In fact, as we've said in several prior posts, Hollywood could do the story a lot better than NASA, with probably a lot more drama and imagination. And Hollywood has the money, too (so do the makers of Grand Theft Auto V).  So Republicans rejoice: you don't have to pay for it with (ugh!) government funds.  Indeed, why bother to actually go to Mars?  Though Hollywood could certainly do it, the studio lots and video game staff could do it much better, maybe even a slight bit more cheaply.

But let's play a bit of a thought experiment game, where genes will actually tell the tale.....

What if NASA's dreams were true--and there really was life on Mars?
Now, the usual kinds of evidence for BioMars takes two tacks, which we've mentioned.  First the rod-like forms in the meteorite--the whole 'microbe' fossils, and second the idea of molecular life-residue that has been sought.

Electron microscope view of meteorite from Mars reveals bacteria-like structure; Wikipedia
Suppose a real, not imagined, microbe were actually found on Mars.  Then the NY Times and Science, really would, for a change, have a story that deserved their typical excitement.  Suppose that, for some reason, the idea that life elsewhere would be just like it is here, and that BioMars evolved microbes.  Hell, if we're going to be fanciful and just extend our rather unimaginative earth-thinking to the entire universe, however implausible and egocentric that is, let's further suppose that sheltered from decay, but at Curiosity-shovel depth, this little Martian bug had DNA in it.  What a genuine thrill (though many would assume this was either a Hollywood stunt or CIA plot)!  But what would it show?

Well, DNA sequences from Mars bugs would be used to reconstruct the time of origin, just as we do with real bugs here on Earth.  What would it that origin time be?  It would have to be more or less what we see on Earth!  Why? Because we know how old the solar system is, and the sun is the energy source for Mars, so Martian life would have to have arisen roughly when it arose here.  Now, let's go further and suppose that life here is, after all, descended from some splattering of living microbes that somehow survived the explosive meteor-borne trip in near-zero degree Kelvin space, from being blasted off from Mars as rocky debris on some sort of volcanic eruption, to survive the entry into Earth atmosphere and land here.

We date life as having a common origin about 4 billion years ago (the Earth being around 5 billion).  So, the common origin of life on Earth, even if it came from Mars, would be as we currently estimate it, and all biology would remain the same as it is now.  We would just make the admittedly fascinating change that the primal soup was there, not here (and that would justify the idea that there must have been liquid water on Mars at the time, etc.).

Now the estimated common ancestral time from earthly creatures is 4 or so billion.  If the Martian DNA sequences didn't seem related to Earthly ones, we would have to consider that life more or less the same as here, arose separately there.  But that makes no sense, really, because if life here were seeded from there, and was just like Earth life (which is why everybody searches for extraterrestrial life that's much like us), then the Martian microbe's DNA would have to look like our estimated early life forms on Earth.  Hardly anything at all would change except, again, the immense fascination of it all (and one might have to rule out that some erupted detritus from Earth was the origin of Mars life).  We could estimate when Solar-system life originated, but perhaps not where.

But what if it's from elsewhere?
Now suppose that we say that Martian bio-like molecules rained down upon it from space, so that Mars life actually originated elsewhere.  Then the time of origin would have to be much older than 4 billion years, because there aren't any remotely nearby stars with planets that could have served as the source, so the splattering ET microbes would have come from light years away, etc.  Their origin time, that we'd reconstruct from their DNA variation (again assuming DNA-like basis and microbe-like parallels to earthly life, which is what everybody's looking for), would be for when life started including the duration of the space journey to here, which means an origin time hugely older than 4 billion years.  And if such stuff reached Mars we'd certainly expect that the same splattering rain from some other star or galaxy would have seeded life here, too.  But our 4 billion time is inconsistent with that. It didn't happen (despite what Francis Crick believed).

Even if that had happened, however, and even if some remnants were to be found on Earth, it would have had nothing to do with life as we know it today, and its origins. Our reconstruction of evolution of life here would not change, because on Earth the common ancestor of all living species is about 4 billion years, so the evolution of what has survived would be just as we already reconstruct it, and would have occurred--and originated--right here at home.

What this means is that, even considering most of the fairly stories being spun, it's hard to see how life on Mars could change anything we know about life--here or there--by very much if at all.  Again, if anything believable like that were found, it would be very interesting, but it's more than a stretch to tantalize us with the kinds of things we routinely see in the media.

If we want a real surprise about life, not just a video game, it will almost certainly have to come from the discovery of something we'd call 'life', truly soaring through interstellar if not intergalactic space to reach us, that's organized and made of something other than our known organic chemistry, not based on DNA, not destroyed beyond recognition on its frigid cosmic-ray blasted way here, with no resemblance to what we see here, or that could plausibly see on Mars.  And no SARS or other microbes.  And how likely is that?

It all seems by far the most likely reality that whether we're alone in the universe, we're alone in the solar system.  And that most lively stimulation we'll get from Mars, is from the candy bar.

If there's a good scientific, or even geopolitical, reason to go to Mars with people or more robots, that's worth the cost, let's discuss it--without the search-for-life red herring.

1 comment:

Cathy Sander said...

I think that biology is a young science compared with physics and astronomy. We still have a long way the go before we even have the slightest clue about what 'life' means...provided that scientific institutions could even exist beyond the 21st century, due to ecological disasters on a global scale that we have self-inflicted upon ourselves.