The Vital Question: Why is life the way it is?

by Nick Lane

But now think of a proton gradient across a membrane. The proton concentration – the acidity – is different on opposite sides of the membrane. Exactly the same difference is found in alkaline vents. Alkaline hydrothermal fluids wend their way through the labyrinth of micropores. So do mildly acidic ocean waters. In some places there is a juxtaposition of fluids, with acidic ocean waters saturated in CO2 separated from alkaline fluids rich in H2 by a thin inorganic wall, containing semiconducting FeS minerals. The reduction potential of H2 is lower in alkaline conditions: it desperately ‘wants’ to be rid of its electrons, so the left-over H+ can pair up with the OH– in the alkaline fluids to form water, oh so stable. At pH 10, the reduction potential of H2 is –584 mV: strongly reducing. Conversely, at pH 6, the reduction potential for formate is –370m V, and for formaldehyde it is –520m v. In other words, given this difference in pH, it is quite easy for H2 to reduce CO2 to make formaldehyde.