"I deliberately avoid having... [a working definition of life]. What I quote... is... from Peter Mitchell... a pioneer... of... , that essentially all cells, with very very few exceptions, are powered by... proton gradients across the membrane. So on one side of the membrane surrounding the cell you've got the high concentration on the inside, a low proton concentration [on the outside]. Protons are... the positively charged nuclei of atoms, so... [y]ou're pumping them out and... putting a charge on the membrane... That's as universally conserved across life on earth as the itself, which implies, as a mechanism, it's very early... [I]t's not something anyone ever predicted. It's not something that... emerges from a chemical understanding of the biochemistry of cells."