This post, pictures excepted, is largely based on the core ideas presented in this paper by Nick Lane, John Allen and William Martin. It's downloadable as a pdf from Nick Lane's website and gives great pleasure in return for careful reading. There are more details on the nature of catalysis in pre protein conditions and the acetyl-CoA pathway in Michael Russell's paper (unfortunately PPV, I have the text) co-authored with William Martin here. Some ideas make a great deal of sense. These are in that category. Enough preamble, on to the post:
The Lizard Peninsula in Cornwall is an interesting place. For a variety of geological reasons a chunk of deep ocean mantle is available to visit on the Earth's surface, without getting too wet or borrowing a deep ocean submersible. We visited Kynance Cove about 10 years ago to pick up a few pebbles of serpentine. We were LC beginners at the time.
Serpentine is formed during the hydration of olivine by sea water, as it percolates in to the earth's crust. The process generates heat, produces molecular hydrogen and increases the volume of the rock by about one third, massively fragmenting it. Sorry for the lack of a hammer.
Large amounts of warm, hydrogen rich fluid are produced under pressure and enter the ocean at hydrothermal vents. The chemistry of serpentinisation also means that the fluid is alkaline. The process is continuous and occurs over geological time scales. These are alkaline hydrothermal vents. I prefer the term of White Non Smokers (rejected by Nick Lane).
Unlike the well known Black Smokers of the mid oceanic ridges/troughs, White Non Smokers generate temperatures and mineral concentrations which are not particularly aversive to the abiotic chemistry which might be considered as pre biotic.
The early Earth is thought to have had an atmosphere, like that of present day Mars, which was CO2 rich. This would have made the early oceans mildly acidic.
White Non Smokers are also structurally full of microporous vents. These have vesicle structures which have warm alkaline fluid within and cool acidic fluid without. There is, intrinsically, a pH gradient across their wall. The difference in positively charged hydrogen ions across the vesicle wall is comparable to the proton gradient across microbial, and of course mitochondrial, surface membranes.
This might be where life started.
If it is, here is the proton gradient, nowadays maintained by the electron transport chain pumping protons, pre dating the development of that chain. Under WNS conditions it is possible to generate high energy molecules using the geochemical proton gradient intrinsic to the vent vesicles. For life as a more distinct entity to leave the WNS suburb simply requires a method to maintain the proton gradient away from the geochemical reactor which initially sustained it.
ATP or, in all probability, a simpler high energy molecule could be made for free in the WNS environment. Away from any "free" proton gradient you need to do work to sustain one. Acetate (like methane) is one of the few products of the exergonic combination of molecular hydrogen (from the vent) with CO2 (from the ocean) which supplies enough energy to maintain a proton gradient in an ATP producing state, without any other energy input, no geochemistry, photons or complex organic chemicals.
There are modern, highly evolved and sophisticated bacteria thriving on this utterly primordial pathway even today. Acetate, to them, is waste. But it can be used if you are so inclined.
As you might expect, activated-acetate (nowadays in the form of acetyl-CoA) forms the basis of most modern metabolism, generating ATP in large amounts through the electron transport chain. But it's probably less primordial than the proton gradient itself.
I think that the mitochondrial inner membrane potential both pre dated life and is possibly rather important to on going life. And you can adjust it, under modern conditions, by what you do or don't eat off of your plate...
Which has some bearing on health.