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Aug 15 2011

Abiogenesis, chirality and narrowing down the alternatives

In the great “mythmaking” that is the scientific process, discovering things about events long lost to history is done a little bit differently than the method might suggest in more mundane circumstances. We develop plausible hypotheses regarding events like the abiogenesis event that occurred here on Earth, and then test them rigorously attempting to falsify each one in turn. Like Sherlock Holmes, or Dr. House, we’ll get to the kernel of the matter by eliminating all the alternatives until we are left with but one plausible truth. We know we’re on the right track when predictions about certain aspects of the theory are demonstrable in laboratories.

We may never learn the exact nature of the exact abiogenesis event that led to us (among multiple possible such events) any more than we’ll know the exact daily routine, shape, facial features, birthday or date of death of the single individual last common ancestor (among multiple possible last common ancestors of that ancestor’s species) between us and chimpanzees, but we know (by genetic and fossil evidence) that we are not that far removed. This should not matter in the investigation of how it could have happened — despite the fact that there are many theories about the event of abiogenesis. We know the first chemicals breached that fuzzy boundary between “mere chemical reaction” and “self-perpetuating chemical reaction” — in other words, between non-life and life — so we know abiogenesis had to happen somewhere. If it didn’t happen here, and we got here by panspermia, then it happened elsewhere in the universe first, but it happened once at the very least.

New research has been very promising as of late with regard to the greatest mystery our planet yet holds, potentially unlocking each of the sub-mysteries one at a time with plausible answers. One of these sub-mysteries involves the chirality of all life on Earth — every amino acid this planet uses as its biological Lego can exist in a right-handed or a left-handed form and would spontaneously form either one at identical odds, but every speck of life on this planet uses only the left-handed version. With our ever-improving knowledge of the early environment of the planet, we’ve discovered that aspartic acid trends sinistral, creating left-handed versions in large quantities in a crystalline structure under those conditions. This certainly does not confirm the theory, but it provides a good hypothetical “seed” that explains how the amino acids that form us all tended to be left-handed.

There’s also the question of why those simple building blocks like aspartic acid might have influenced the other amino acids that self-generated in the environment to follow suit in their chirality. So, scientists built on the earlier result and introduced the left-handed acids into an environment with equal proportion left- and right-handed amino acids, and found the left ones crystallized much like the aspartic acid crystal in the earlier experiment.

“These amino acids changed how the reactions work and allowed only the naturally occurring RNA precursors to be generated in a stable form,” said Hein. “In the end, we showed that an amazingly simple result emerged from some very complex and interconnected chemistry.”
The natural enantiomer of the RNA precursor molecules formed a crystal structure visible to the naked eye. The crystals are stable and avoid normal chemical breakdown. They can exist until the conditions are right for them to change into RNA.

This experiment had every possibility of falsifying the earlier hypothesis but it did not. More research will either disprove both these hypotheses, or confirm them repeatedly over many iterations until our confidence level has increased so that they’re the best plausible explanations. Or, who knows? Perhaps we’ll one day unearth some new evidence, and we’ll need a better explanation to incorporate that new knowledge.

That’s how science works.

2 comments

  1. 1
    George W.

    In a way I can sort of understand the trepidation of an informed Creationist about scientific endeavors to recreate abiogenesis.
    In your previous article Jason, you said, and I quote:

    The problem comes down to one of narrowing — if we know the early Earth had to have ammonia (to provide the organic compounds necessary), then we’ve excised all models that do not include ammonia. Scientists later discovered a photochemical reaction of nitrogen that would provide this ur-Earth with the necessary ammonia.

    We seem, by your statement, to know that the early earth had ammonia because it was necessary as a precondition for the organic compounds- and this seems to assume the very thing you are seeking to prove- that the building blocks of life were there for the taking, leading to the spark of life.

    All that said, I think there must be ways for science to prove this simple fact, and the absence of a slam dunk case ought not discourage scientists from doing the theoretical legwork early.

    Regardless, I think that proof that under the right conditions (assuming they are possible and all the better if there is a range of conditions) life could have arrived “spontaneously”, or in fact it is likely that it would, then I feel like this is something that narrows the necessity of a creator- not necessarily the existence of one, but certainly the necessity to postulate one.

    The issue comes down to the Creationist, who can defensibly still make the statement that “It is impossible for life to spring forth unaided” being forced to change the statement to “It is unlikely that life sprang forth unaided, even if it is entirely possible”, which will mean that we’ll get to witness the perpetual abuse of probabilities that we already see in evolution become all the more common and complex when discussing abiogenesis.

  2. 2
    Jason Thibeault

    Nice bit of devil’s advocate. You’re right, that’s very likely exactly how they’re thinking, and I’ve gotten that sense off of Anthony McCarthy, that his chief issue with this research is that we don’t have the level of certainty down to a science, with the sub-issue of the fact that we narrow down the possibilities in part by eliminating the impossible in absence of direct physical evidence for those certain conditions. The fact that we know ammonia was involved because it had to be, indicates that we don’t have direct physical evidence that ammonia was involved, and thus we are engaged in building a narrative without direct physical evidence. My issue with that is, we — the life on this planet, who exhibits chirality in our amino acids and is built out of the same seven “organic” elements across the board — are evidence. The fact that we all work the same way indicates that whatever scenario we hypothesize and test must result in life that exhibits the characteristics that make us us.

    You never know. In a far-flung Star Trek universe, we may start encountering enough life on enough other planets that use different elements, that have right-handed chirality, that build different amino acids, that metabolized before they reproduced or vice versa. We might discover that the parameters within which life can emerge are actually very forgiving, and that different sorts of life will emerge under different sets of conditions. We may experiment with our hypotheses and discover that every single one of them is plausible because this universe is practically teeming with life, if we could somehow survive the void between us to examine it all.

    Or, we could discover that none of the ways we’ve hypothesized can, under any circumstances, lead to life, and that the event must therefore be an ex nihilo divine intervention. I strongly suspect the fact that we’ve been failing to falsify any of these steps is what’s really getting on the theists’ nerves, because with each plausible link in the chain, that last possibility becomes more and more remote.

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