Tuesday, March 1, 2016

Early Origination of Life – Organic Oceans – Part 3

http://stanericksonsblog.blogspot.com/2016/02/early-origination-of-life-organic-oceans.html and Part 2 of this subset of posts detailed a different theory for the origination of life. The theory came into being because it was asked, what conditions might have been different in the early days of planet Earth, when life did originate. One condition, which vanished sometime after that, was the possible existence of bodies of organic liquids, possible a melange of all the ones which were either immiscible with water, or much preferred an organic solution to a water one. This of course means the relative solubility is much different, not that the particular organic was wholly insoluble in water.

The concept of an organic ocean is remarkably simple. An organic ocean exists when there are large quantities of organic compounds on a planet, and they liquify at whatever temperature the planet is providing for them. Planets probably start out hotter, because they are formed from gravitational infall, plus planetesimals crashing into them at incredible speed, and between the heat generated by the gravitational infall plus the heat generated by the great compression caused by the thousand of kilometers of mass, together with the heat of impacts, the whole planet would start out hot. Then, like everything without an internal source of heat, it cooled down. And as the condensation point of each organic was passed, in the downward direction, it would join in the organic ocean. Once the condensation point of water was formed, there would be both organic oceans and water oceans. Likely, the organic ocean would overlay the water ocean, from a guess at what the density of the organics would be.

Various things happen. One thing, the only really interesting thing from the origin of life point of view, is that there would be a meniscus, and certain molecules would have a preference for staying on it. These are molecules, perhaps longer than most others, with a hydrophilic molecule on one end, and a lipophilic one on the other, hence the name ambiphilic. One interesting question is that if there are more than one variety of ambiphilic molecules in the dual ocean, would they tend to segregate, or somehow collect in like groups. Another one, and a critical one, is would there be any of them which would adhere to like molecules, leading to the formation of a flexible membrane.

The organic ocean hypothesis for the origin of life assumes such a membrane can exist, and then molecules of other types can attach to them. This provides a high density and perhaps some orientation preferences for molecules. There is also assumed to be a set of molecules which interact with each other, as well as the membrane, and as well as with ions reaching the membrane from the water side, and are able to replicate themselves.

Thus, instead of having to solve the very difficult proposition about a cell membrane forming from chemical processes alone, some physical chemistry is brought in to help, and it is not the responsibility of the replicating chemicals to produce it. This makes it easier to find some set of molecules that, under some conditions as described in the organic ocean hypothesis, can make other molecules which include their own types.

This isn't life, of course, as it doesn't meet the definition of life that is current now: something is alive if it can reproduce, feed, avoid damage, and adapt to change. That does seem to be a tall order, but labeling these chemicals as alive is really a meaningless distinction. What does matter is the existence or non-existence of a pathway to more complex collections of molecules. Specifically, is there such a thing as chemical evolution?

If there is chemical evolution, then the endgame of the organic ocean hypothesis is obvious. Each generation of the set of molecules which can replicate, albeit in the unusual situation of being attached to an ambiphilic membrane located on the mensicus between a water ocean and an organic ocean, has the chance of some change being induced by any of a wide variety of events, and some of these changes will be successful. Non-lethal is not the right word for a non-living thing, but that's the idea. Some successful changes will be more prolific and numbers will favor them.

Sooner or later, there would have to be some mutation which makes one component of the membrane, and maybe later, both components. Once that happens, the number of membranes goes up, and the latest version of them comes equipped with some set of molecules which makes their components. Do they reproduce now? Yes. Do they feed now? Yes. Do they avoid damage? No. Do they adapt? No. Two out of the four criteria for life isn't a bad start.

Consider the avoiding damage criteria. Exactly what might be causing damage to this weird little collection of molecules, or single gigantic molecule as they are all joined together one way or another. Chemicals might. Some chemical in the water side might break bonds of the molecules on the organic side. If the membrane had selective porosity, so that damaging ions or ionic chemicals or whatever bad stuff there was, couldn't get through, but the useful ions that involved providing energy to the whole gang of molecules or contributed to the construction of a copy, could get through, it would be remarkably superior in replication power. Chemical evolution just came through and provided the third criteria.

As for damage protection, there might be some molecules on the organic side which might disassociate something in the molecule set, but, since there is no membrane of the organic side to protect the molecular machinery there, no damage protection can go on. Unless, of course, the membrane bends around and closes. As long as all the needed molecules can get through, but the ones which disassociate, or even get in the way by attaching to some critical juncture where something else was supposed to attach, cannot get through, we have damage protection in spades!

We also have something which has one more characteristic of a cell, an enclosing membrane. It isn't alive, as the fourth criteria isn't met, but it is beginning to appear like life.

Can chemical evolution happen? Can it happen in some situation which is completely advantageous for it to happen? Perhaps chemical evolution cannot happen in any situation on Earth now which exists anywhere on the planet, but it could long ago. There is no clear boundary between chemical evolution and biological evolution, so if chemical evolution can happen, there seems to be no reason why it cannot continue on past the point where it has graduated to life and biological evolution.

If I had a big physical chemistry lab, and I wanted to find out about the origin of life, under the organic ocean hypothesis, I would start by experimenting with solubility, so it would be possible to figure out how any combination of molecules would divide themselves up. Much is known about solubility, and some general principles are that like dissolves in like, meaning that non-polar molecules are likely to dissolve in any bath of non-polar molecules. But what kind of exceptions arise?

The next thing I would do would be to make a catalog of ambiphilic molecules, and see how may hundreds or thousands there are. Do they segregate into groups? Do those groups tend to bond, or if there were any particular things on the water side of the meniscus, like an ammonium ion or anything else, that would cause such a bonding? Is some unique molecule from the organic side needed to form such a bond? This sounds like good fun for physical chemists.

What things, say starting with amino acids, like to bond onto some of the lipophilic ends of these molecules? How stable is the bonding? Again, is it mediated by something from the water side, the organic side, or both together?

After a whole lot of physical chemist-years of work, it would be time to search for replicating combinations of molecules. Once that is found, chemical evolution would be as good as proven, and the origin of life would be in the headlights, straight ahead.

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