Friday, March 18, 2016

Early Origination of Life – Organic Oceans – Part 7

The Theia alternative for the theory of life having originated in organic oceans in the very early Earth has these oceans created, or at least added to, by the cataclysm that occurred when the moon was formed, specifically by the impact of another large planetary body with the predecessor to Earth. The key idea is that there were organic chemicals in large amounts on the Earth, and the immiscible ones formed their own pools, termed organic oceans, and in many cases, these organic pools laid on top of water pools. Perhaps the scale was that of oceans, or perhaps only of lakes.

Having an ocean of a certain group of organic compounds doesn't obviously lead to life, but what it does lead to is the collection of some key organic compounds on the boundary between the organic pools and the water pools, ones which are long with two dissimilar ends, one being hydrophilic and being drawn to the water side, and the other end being lipophilic and being drawn to the organic side. These ambiphilic molecules are very similar to the membranes that make up cell walls, and also to DNA-like molecules.

In all theories of the origination of life, statistics plays a role. There is no set of chemical reactions that inevitably produce a cell. There is no solution of molecules which deterministically forms a replicator molecule, which is one of the key features of any origination theory. These things all have to occur as a result of a series of steps, many of which are statistical. A slew of different molecules can be in a solution, and they randomly interact, sometimes and almost all times, just coming close and then drifting apart, and very occasionally, some chemical change happens. The molecules can come from directions where they do not interact, or can come into contact with the wrong corner or edge of the molecules touching each other, or very occasionally, the orientation can be close enough to the ideal one and they interact. They can rest close to each other for a short interval of time, before being jostled apart by the kinetic interaction with solute molecules, or, very occasionally, they can stay together long enough for the chemical transformation to occur.

For each of these reactions, there is a time that arises, which is the time necessary for the reaction to occur, given all the conditions which affect it. Linearity usually prevails, so that if the reaction is of two molecules joining, the time necessary for one combined molecule to form, on the average, is proportional to the number density of the first molecule and the number density of the second molecule. In short, if there are twice as many of molecule A, the average time to create molecule AB is half a much.

There are a great many possible theories of the origination of life, and each of them has one or more interaction times that together provide an estimate of how long the whole process would take. Imagine a theory that involves organic molecules in a water solution eventually joining up to make a self-replicating DNA molecule. Just assume such a thing is possible. If the time required is a thousand trillion years for the first molecule to be formed, say in an ocean the size of the Pacific, this is not a theory of the origination of life. The interaction times have to be substantially less that the lifetime of the universe, the planet they are assumed to operation on, and the oceans themselves. One aspect, therefore, of a successful theory, is the devising of phenomena which will expedite the transformations, meaning, cutting down the expected time for them to happen.

One way is to increase the number density of those molecules which have to play roles in the different steps of the process. In those theories which involve sea vents being the venue of life origination, figuring out some way in which organic compounds of many different ilks were concentrated in the sea around these sea vents would cut down the times. But such a concentration doesn't seem to have any physical basis for it.

The organic ocean theory does have such phenomena. Consider a ten meter column of organic compounds, with ten thousand molecules of special importance in it. The average distance between such molecules is about 17 centimeters. Now compare the situation where these ten thousand molecules are precipitated down to the square meter of meniscus at the bottom of the organic ocean. Now the average separation is about 1.4 centimeters. These separations are a measure of how frequently such molecules would interact. A factor of ten is available from having the molecules resident on a meniscus between the organic ocean and the water ocean.

Interaction times for this scenario is actually the sum of two times; one is the time necessary to get the important molecules down to the meniscus, and the other is the time necessary for random kinetic activity to bring them together. The distance measure only relates to the last of these. How does the first one become shortened?

When the Theia planet hits the proto-Earth, a huge amount of rock is vaporized and it hangs in the atmosphere for times of the order of years. As the atmosphere cools down, and the organic oceans form, this dust would drift down into the organic ocean, and enter it from the top. Nanoparticles of rock dust do not sink like large rocks, but they drift downward. If the interesting molecules adhere to these dust particles, they could be transported downward much faster that they would simply do a Brownian motion to get to the mensicus. In essence, there is a supplemental transport mechanism that would exist during the short period following the Theia impact.

If there was dissolved gases that resulted from that impact, and they were in the seabed, as well as in the water, gas molecules would gradually find each other and when enough were collected to make a microbubble, bouyancy would cause it to drift upwards. If such motions could entrain molecules that were in the water ocean but were ambiphilic, they would be swept upwards. The lipophilic, read hydophobic part, of these molecules would be happy to poke into the gas bubble, leaving the hydrophilic ends to remain in the water.

Thus there are mechanisms which might reduce the time needed for life origination in the organic ocean and Theia hypothesis. Quantitative results would be nice, but for now, understanding some mechanisms might exist helps reduce credulity.

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