image: l*u*z*a*
Because this is FQXi, I want to post another radical suggestion - this time related to the possibility of life on the moon.
Before I do, though, one reader has asked a reasonable follow-up question to the last post: why was NASA ever concerned about "lunar germs"? How could microbes have gotten to the moon in the first place?
About NASA's quarantine program back in the Apollo years, or why it was eventually dropped, I have no knowledge (anyone who has, please chime in). My guess is that lunar infection, even if it didn't seem likely given everything we knew, was given some non-zero probability simply on the grounds that we didn't know a whole lot.
As to how life *might* have gotten to the moon, two ideas present themselves. The first, while by no means mainstream, is hardly fringe any more. The second is my radical idea for the month.
I had the pleasure once of speaking with Cassie Conley at NASA, whose experiment onboard the ill-fated Columbia showed that even macroscopic life-forms can survive not only the mechanical stresses of explosion and impact but the burn of falling to earth from space. "Transpermia" is the suggestion that life hops from one Solar System Object to another inside chucks of debris, blasted, say, off a planetary surface by an impactor or extremely powerful eruption. The life-bearing asteroid then drifts in its own orbit until it happens to be drawn into the gravity well of another planet which, if it is hospitable, becomes the microbes' new home.
Could our own moon have collected guests, the same way it presumably collected ice? The moon, having essentially no atmosphere, is subject to direct collisions that don't even burn "on the way in." Earth-crossing asteroids stand a reasonable chance of hitting it, as evidenced by its densely pock-marked surface. Plus, there have been billions of years of collisions taking place up there. If transpermia is correct and if even a small number transferred biota, they could conceivably still be snoozing in the centers of what we see as impact craters. Extremophiles are already on record as being able to lie dormant for millions or even tens of millions of years. Transpermia traces on the moon are a stretch, but not an absurd one.
image: largerich
Now the more radical idea: Where else could lunar microbes have come from? I'm improvising here, but . . . what about Earth itself?
We know --- or, at least, it's a well-reasoned theory - that the Moon was formed when a titanic, Mars-sized impactor hit the early Earth, blasting enormous quantities of mass into orbit. Let's assume that theory is correct: most of what was ejected would be molten, but not all of it. Suppose life had already gotten started on Earth at that time. Could the same process that formed the moon have sterilized the young planet's surface and transferred a sample of its biota into orbit in one go?
Think about it. Endoliths safely housed deep inside some rocky mass, tumbling around amid a wash of superheated detritus, protected from the various environmental hostilities until, eventually, the moon coalesces into a quiet orb.
I should repeat that this is pure speculation on my part. But if anything like this were actually the case, then NASA's "lunar germs" might be our oldest living relatives . . . or something even more interesting.
How so? Evolution may have started over again several times during the bombardment period on Earth, with its products being wiped out with each new impactor storm and then arising anew from organic scratch. In this scenario, the products of one of those early attempts could have been preserved inside rocks in parts of the moon. If so, they would be the only life forms indigenous to Earth that nonetheless are unrelated to the life forms that gave rise to us--indeed, to everything that has existed in what we call the tree of life.
We have never known whether winding the clock back and starting evolution over again on Earth would produce the same kinds of living things, the same solutions to environmental needs, the same basic structural patterns. It seems unlikely, though. There's no compelling reason to assume that what has evolved here *must* have evolved--rather, the current biological situation is probably just what happens to have come about. Roll the dice again and you would no doubt see convergent forms, but not wholesale repeats. There are plenty of ways to skin a microbe, and small differences at the beginning could lead to enormous, even unrecognizable, dissimilarities later on.
So if we had fossil evidence, to say nothing of dormant or active samples (!), of "pre-biosphere" Earth biota . . . what might it be?
RNA life? Expanded alphabet DNA? Non-carbon based microorganisms? Or something even stranger?
To find lunar neighbors might be not a threat at all -- but an amazing opportunity to understand our own evolution.