In part 1 of this subset of posts, the idea was touted that in the early days of planet Earth, there wasn't anything around to consume carbohydrates, and there were a lot of them. They formed a layer on top of the water oceans and lakes and some very interesting things happened, over some tens or hundreds of millions of years. Specifically, some hydrophobic chemicals residing in the organic side of the meniscus between the layers got linked with some hydrophilic chemicals residing on the water side of the meniscus. This particular combination would have no choice but to remain at the meniscus. With enough of them around, and some intermolecular attachment, a membrane could form.
Provided they were stable, these membranes could collect and build up in numbers. One pathway to go forward with a hypothetical method for life origination would have the membranes becoming spherules, and here is some primitive cell. But perhaps life origination theories try to rush too fast to making cells. Maybe there are a few intermediate steps, all reasonable chemically.
What are the possible interactions between a molecule and such a membrane? If the molecule could attach itself to the preferred side of the membrane, then it might do other things. Do you see the looming shadow of the hero of some life origination theories, the Replicator? This is a molecule which makes a copy of itself. Of course, maybe there is a molecule which, when attached to a membrane, can make a copy of itself. Or maybe there is a more complicated set-up, where molecule A, when attached, makes molecule B, and molecule B makes molecule D, which is transformed by something connected to the membrane into molecule C, which is then transformed into molecule A, beginning the whole conga line again. Does such a membrane provide a convenient collection point for a number of molecules, the majority of which just attach and maybe detach later on, and a few which make something else, like serial copies of some other molecule, which begins a series of transformations, mediated by the membrane or various things which have attached to it, into the starting point? If only one of the steps is a one-to-many transformation, such as molecule Z turning some common constituents of the organic ocean into molecule Y's, then there is replication.
On the water side, the ocean would have a lot of ions, sodium, potassium, chlorine, ammonium, phospate, sulfate, calcium, and scads more. Water is a polar molecule and just loves to break up salts and compounds and separate the pair that makes them up. What happens when an ion of some type is blown into the water side of the membrane? Does it alter the membrane? Does it osmose through it and start making changes to things hanging on the other side of it? Does it slip through a crack in the membrane and interact with things from the other side? Does it move some protons around and transfer energy to something on the other side? It sounds like a little chemical laboratory.
What happens if there is some molecule or set of molecules that can reproduce itself? We are talking about molecules which attach to the meniscus membrane, which may provide the mechanism for one or more of the steps of copying, or just to attract some ion to the membrane which can slip through it to be used on the other side. What happens to the copy? Since the molecule or molecules like to attach to the membrane, and one was handy, it would, and this would go on until the attachment points were filled up. Now we have a doubly-thick membrane, formed by the original stuff which was hydorphilic and hydrophobic, like soap, with a second layer of things which can reproduce using the membrane. What can happen with this more complicated membrane?
Perhaps we should consider the options. If some molecule from the organic side attaches, and some ion from the water side sidles through the membrane and makes a change in the molecule, like becoming part of it, we have layering going on without the need for any replication. This assumes there is plenty of that particular molecule in the organic broth. So layers might form, homogenous or heterogenous, and even a third layer or more.
There doesn't have to be just one type of membrane occupying the meniscus region. There could be ten or fifty varieties. If only one is capable of attaching many interesting organic molecules to it, then that one could be the one that initiates life. Suppose it can attach many amino acids, which might have been made by other membranes. They can combine and separate, and do whatever amino acids like to do, until there is one combination which just happens to make copies of itself. So, one of the membranes might serve as a way of speeding up chemical combination, which eventually leads to replication. No cell has been made so far. No membrane has closed in on itself to make an inside and an outside. They have just stayed where their hydrophilic and hydrophobic halves are thermodynamically better off.
It sounds like some chemists could amuse themselves finding out which membranes attract many different types of organic molecules, especially and most importantly, complicated ones. If there are some, we are two steps closer to understanding the origin of life. The first step was having an organic ocean and a meniscus, where certain types of molecules could hang out, and form membranes on the molecular size scale. The second one is having one such membrane serving as a combination zone, where different molecules would be put in proximity, and perhaps would interact.
It is going to take many steps to originate life, but what we see here is a possibility for chemical evolution. Once there is an environment, like a meniscus-inhabiting membrane, where various combinations of attached molecules might occur, the one which replicates the most easily would win out, barring stability problems. The concept of the organic ocean provides both the concentrated environment for such chemical evolution, but also a feedstock which may have plentiful amounts of whatever has to be consumed in such a replication.
There really may be nothing that would prevent some replicator molecule from forming in the liquid ocean itself, except time and probability. Just try to think of two molecules in a dilute solution getting together at the right orientation and joining. Then compare that to a membrane which provides a location for the contact, other feedstock items, some ions to incorporate, some energy to make use of. It could be that no matter how many opportunities for a replicator to form from two component molecules happened in the liquid ocean, the joining never takes place because of some mediation the membrane provides.
Real cell walls do all of the things the hypothetical mensicus membrane might do. The problem for chemistry is simply to show that membranes can form, likely of simpler nature than the phospholipids of a real cell wall, and perform these same functions. How simple can it get?
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