Thursday, March 31, 2016

Early Origination of Life – Organic Oceans – Part 10

The organic ocean idea is based on the existence of large amounts of organic compounds on the early Earth, including many which are immiscible in water and would form their own ponds, lakes, pools, or more importantly, layers upon a water body. It goes on to assume that some ambiphilic moleculess would be formed at the meniscus between the two liquids, and some of these would have sufficient mutual intermolecular forces to cause them to link together, forming some continuous areas. Then the idea includes the idea of a intermediate organic molecule which can insert itself between the two halves of the ambiphilic molecules in the membrane and which can also catalyze other copies of the same molecule to insert themselves into other copies of the same ambiphilic molecule. This meets the definition of a self-replicating molecule, and chemical evolution would take over from here.

One principal alternative was that these organic compounds were created during the impact of a planetoid onto the proto-Earth, which led to the formation of the moon. The impact itself would create many of them and the resulting very long period of volcanism, when the new core settled down, would add more. Complex organic molecules can be thought of as simply another form of higher energy state, the population of which would be vastly increased by the heat generated in the impact and the volcanism.

To create a theory of life origination, it would be nice to foresee that there are possible next steps that would lead, eventually, to something having the attributes of organic life, which might include the existence of an entity, rather than simply patches of membrane made of one or more interesting molecules. Some potential next steps would be having different intermediary molecules, assuming more than one can catalyze its own insertion into the ambiphilic ones, which are assumed to form independently. Perhaps the membrane has a natural curvature, with the lipophilic side being smaller in cross-section, so that there would be a tendency to curve and eventually close. There would have to be permeability to various molecules coming in or going out, as the membrane at this point is simply a means of concentrating populations to increase the reaction rate.

Life, and chemical evolution, need energy to function. The initial impact would produce many molecules from which energy could be extracted, as could the volcanoes. The initial intermediary molecule, the self-catalyzing one, would evolve to other ones, and later migrate some component to the end of the hydrophilic end. Then some molecular component might be added on which would serve as an energy transport, taking energy from one or more kinds of molecules floating in the oceans and storing it until it became time to use it in the replication process. If the membrane closed upon itself, one next step would be for some components to float freely in the interior of the membrane, while others stayed attached.

If there was some inherent curvature present in the membrane, then as it increased with more ambiphilic molecules being inserted into it, it would buckle and perhaps separate into two. If one new membrane-enclosed volume was lacking copies of some key molecules that were the product of chemical evolution, this budding would be a failure. If the density of the key molecules was high enough so that all of them had copies inside both pieces, we have an instance of reproduction. Perhaps it could be called a cell at this time.

It is all well and good to originate life in a temporary situation, but there has to be enough time for chemical evolution to allow for the occurrence of two things we know happened on early Earth. One is that the organic pools disappeared, leaving only water bodies. If by this time closed membranes had evolved, and they were able to function wholly in the water, without contact with the meniscus, then whatever simplistic form of life this is could continue. The second thing that happens is that volcanism stops, or almost stops. Perhaps there are still some vents in deep ocean areas, and some volcanoes under the sea busy erupting from time to time, but nothing like the maelstrom that existing for millions of years after Theia, the impacting planetoid, hit the proto-Earth.

Without volcanoes, what is going to produce molecular energy for the simple cells? There are only two energy sources possible, photons from the sun, and chemical energy from the deep Earth or from some exposed rocks. There may be some primitive cells that absorb and consume other cells, but there has to be some energy entering the domain of life; it is impossible to have an area with only carnivores – something has to get energy from another source. Either some early form of photosynthesis, or rather simply photon absorption into some stored energy form, had to have evolved before the volcanoes died down, or the chemotrophs would have to retreat into some small areas where there were still sea vents or other sources of chemical energy. This would represent a drastic chokepoint for life on Earth, but certainly not a definitive reason for extinction.

If volcanism did not go on in one area long enough for photon absorption to evolve, it would be necessary for these primitive cells to migrate to another area. There is no process that would end the existence of such a cell. If it did not encounter any substances it needed to continue to grow and even bud, it would not shrivel up and die, it would just keep floating around in the ocean until some event happened to destroy it, or it floated into an area where there were the right kind of organic molecules that would permeate through the membrane and allow it to resume functioning. There were no predators, no acid areas as far as is known, no high temperature regions, and in short, not much to destroy the little cell. A lightning bolt at the right time and place could certainly do it, but the probability of that is low, and ocean depths might serve to limit the possibility of such damage.

What this implies is that life origination happens and early chemical evolution happens and even the first steps of the most primitive cellular evolution happens relatively quickly, when there are massive amounts of organic chemicals around, including many possessing extractable energy. After that, evolution slows way down, until at some later date photon absorption becomes possible. Then it speeds up again.

Some key questions related to this hypothesis about the origination of life are: is it possible to develop organic oceans in large volumes except via the impact of a planetoid; how long would extensive volcanism last after such a major rearrangement of the mass of the planets involved; what would be an estimate of the rate of formation of the first cellular structures following the meniscus membrane concept. Another one would be: is there any possible signature still present on Earth that could show if there was a period when there were organic pools present on Earth.

If the answers to these questions come back to favor the organic ocean/Theia impact hypothesis, we may be the only life in the galaxy. Perhaps orbital simulation of possible early solar systems could tell us if it is extremely rare to have such an impact, or if we are going to be surprised to find that impacts like this are almost as common as exo-planets.

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