Four kilometers down in the Pacific, on a plain that never sees light, the seafloor is scattered with lumps of metal the size of potatoes. Manganese, mostly, with iron and nickel and cobalt, grown over millions of years a few millimeters at a time around a fleck of shell or shark tooth. Polymetallic nodules. They’re what the deep-sea mining industry wants.
A couple of years ago a team sealed chambers over patches of this seafloor and watched the oxygen inside go up. Not down, the way it should in a closed box full of things that breathe — up, to three times the background level in two days. The proposed explanation is that the nodules act like little batteries. Measured across two of them sitting near each other: about 0.95 volts. It takes around 1.4 to split seawater into hydrogen and oxygen, and clustered nodules might get there. Oxygen, the thing we file under sunlight and photosynthesis and the surface, being made in total darkness by rocks. The first author says he spent years assuming his instruments were broken before he let himself believe it.
That’s the version that makes the headlines, because if it’s true a basic line in the biology textbook is wrong — oxygen on Earth doesn’t require life or light, not all of it.
But here’s the part I keep turning over. The challenge to it is just as concrete, and almost smaller than the claim deserves. The critics point out that chambers with no nodules in them at all also showed oxygen rising — which shouldn’t happen if nodules are the cause. And they have a candidate culprit: a trapped air bubble. On the order of a tenth to a fifth of a liter, caught in the lander as it sealed, slowly leaking its oxygen into the chamber under crushing pressure. A fifth of a liter of ordinary air would account for the whole signal.
So right now, this June, the thing is suspended between two readings that could not be further apart. Either rocks generate oxygen in the abyss and we have to redraw where the breathable world begins, or somebody trapped a bubble. Nature Geoscience has attached an editor’s note of concern to the original paper. Expeditions are going back down this year with better controls to settle it.
I find I don’t want it resolved yet, which is probably the wrong thing to want. For now the same measurement is a rewrite of the planet and a fifth of a liter of trapped air, and nobody on Earth can tell you which.