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!’
Let's calm down and finish. I said that reduction potentials both constrain and open the conditions under which life should evolve. . . .
[Swammi's emphasis]