I have been reading Nick Lane's fascinating book The Vital Question; each page is power packed with so much new (to me) information that I am reading it very slowly.
Without a high flux of carbon and energy that is physically channelled over inorganic catalysts, there is no possibility of evolving cells. I would rate this as a necessity anywhere in the universe: given the requirement for carbon chemistry that we discussed in the last chapter, thermodynamics dictates a continuous flow of carbon and energy over natural catalysts. Discounting special pleading, that rules out almost all environments that have been touted as possible settings for the origin of life: warm ponds (sadly Darwin was wrong on that), primordial soup, microporous pumice stones, beaches, panspermia, you name it. But it does not rule out hydrothermal vents; on the contrary, it rules them in. Hydrothermal vents are exactly the kind of dissipative structures that we seek – continuous flow, far-from-equilibrium electrochemical reactors.
We have established on thermodynamic grounds that to make a cell from scratch requires a continuous flow of reactive carbon and chemical energy across rudimentary catalysts in a constrained through-flow system. Only hydrothermal vents provide the requisite conditions, and only a subset of vents – alkaline hydrothermal vents – match all the conditions needed. But alkaline vents come with both a serious problem and a beautiful answer to the problem. The serious problem is that these vents are rich in hydrogen gas, but hydrogen will not react with CO2 to form organics. The beautiful answer is that the physical structure of alkaline vents – natural proton gradients across thin semiconducting walls – will (theoretically) drive the formation of organics. And then concentrate them. To my mind, at least, all this makes a great deal of sense. Add to this the fact that all life on earth uses (still uses!) proton gradients across membranes to drive both carbon and energy metabolism, and I’m tempted to cry, with the physicist John Archibald Wheeler, ‘Oh, how could it have been otherwise! How could we all have been so blind for so long!