Just exactly how would Earth Science go about figuring out if a theory of life origination was correct? By Earth Science I am trying to convey the efforts of whatever specialty of science was needed, as different theories might have different needs.
Is this an unknowable, because science doesn't have the tools available to do whatever is necessary to validate a theory, or to pick among its options to find one that works? Will it stay an unknowable for 10 or 20 or 50 years because there is no momentum visible now that will fill in the gaps quicker than that and come up with the knowledge needed to make a good assessment?
Consider the organic oceans hypothesis. The essence is that an ambiphilic molecule, part hydrophilic and part lipophilic molecule, located on the boundary between two immiscible liquids, one water-based and one with an organic solvent, could insert a molecular component into a shorter molecule. The shorter molecule was just the two ends, the hydrophilic and the lipophilic ends, joined without the intervening molecular component. This is the absolute minimum action necessary to constitute replication, and then feedback from number amplification and chemical evolution take it from there.
Notice that the entire burden of this concept has been shifted away from the design of the replicator molecule, leaving it only a template with a bit of catalytic capability, very specific in fact, to the conditions that enable the replication. They carry the load, and it is a diverse load. First, the meniscus has to exist, meaning there has to be enough organic molecules around to make up pools of liquid. Some process has to make these molecules. If that isn't hard enough, some process has to make predecessor molecules similar to the replicator molecule but lacking a central component. The central component has to be available in sufficient numbers. Perhaps there are conditions on one or both of the liquids in order to enable to matching of the replicator's template.
Now comes some organic chemist who wants to test the theory. He can try to test the replicator portion of the theory, which is the simplest part, by coming up with as many combinations of hydrophilic and lipophilic molecular components as he can, and then as many central molecular components, and try to figure out if there were any conditions that would enable the replication. At this point, the combinatorics are going to ensure that his entire career might be spend trying out different combinations, without even getting through the list. Here is the essence of the dilemma. Once biological life began, all these chemical evolution early stages disappear, and there is no way to project backward from the very complicated organic cells to what was the initial replicator, a simple molecule. Maybe there were ten or a hundred chemical evolution steps before anything like a cell appeared. No fossil residue exists; nothing at all is around to provide a hint as to what happened in detail.
There are some constraints that would help to reduce the combinatorics. Each end of the predecessor molecule is supposed to have good intermolecular attraction to a copy of itself, at least if oriented properly. For the hydrophilic end, that probably means some polar attraction in a particular geometry. Similarly aligned polar molecules would have to have the polar separation along an axis perpendicular to the longitudinal axis of the molecule, so that with proper rotation, we could have positive near negative and negative near positive. On the lipophilic end, there is likely nothing but London forces, meaning that the molecular component and a copy of it would have to fit closely together. Long carbon backbones would do this, but so would many other arrangements of chains and rings. So our chemist is still facing a lot of long nights examining different combinations.
Another requirement might be that the coupling between the hydrophilic end and the lipophilic end might be rather weak, so that the splicing in of some intermediary molecule can be accomplished without too much energy. Having the coupling be through a single carbon atom, rather than through a ring or other structure would mean that the two ends could rotate relative to one another rather freely. This would mean the polar end could align itself with the proper charge distribution, and the non-polar end could align itself with the proper geometric arrangement, each without affecting the other end. This might not be necessary, if the only possible arrangement between two strongly structurally coupled ends was the one that matched other molecules well. It is just a matter of more options.
If the chemist is an experimentalist, he can come up with a few hundred ideas as to molecular combinations, and then check to see if they have strong intermolecular forces. It is not readily possible to measure the force that one molecular component has on another, but there might be some surrogate. In a bath with a meniscus, such as the one described in the organic oceans theory, such ambiphilic molecules should line up on the meniscus, properly oriented, and form a film. With some luck, the film would be detectable, and perhaps some estimate of its tenacity could be made. This might be related back to the individual intermolecular forces.
Wouldn't it be ever so much simpler to have a computer figure out the intermolecular forces? Unfortunately, this is not quite possible yet for the wide range of molecular components that need to be examined. If they could be calculated, solubility could be calculated with something better than empirical fits. Melting and boiling points could be calculated, instead of measured. Making these forces into routine calculations, so that our organic chemist could just input some of his favored molecular components and out would come the forces, is just what is needed for this first and simplest step of validating the first and simplest part of a life origination theory. The previously thrown out numbers, ten, twenty or fifty years might be possible estimates of how long it will be before Earth Science can do this. Then all the hard stuff of a life origination theory can be tackled.
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