[This is maybe the single most fascinating piece of biology research I’ve ready about in years. 2010, so it’s probably old news to some. -egg]

The discovery that ATP synthesis is powered by proton gradients was one of the most counterintuitive in biology. The mechanisms by which proton gradients are formed and coupled to ATP synthesis are known in atomic detail, but the broader question – why are proton gradients central to life? – is still little explored. Recent research suggests that proton gradients are strictly necessary to the origin of life and highlights the geological setting in which natural proton gradients form across membranes, in much the same way they do in cells. But the dependence of life on proton gradients might also have prevented the evolution of life beyond the prokaryotic level of complexity, until the unique chimeric origin of the eukaryotic cell released life from this constraint, enabling the evolution of complexity.

Source: Proton Gradient, Cell Origin, ATP Synthase | Learn Science at Scitable