nodules

One specialized subset of transcription initiation sites the group found was in root nodules, a structure on legumes' roots that harbors interaction between the plant and Rhizobia bacteria.

In the 1960s, an American mining engineer named John Mero publicized a tantalizing idea: that these nodules were an untapped fortune ready for the taking.

The bounty for such mining operations are polymetallic nodules — mineral spheres that are roughly the size of a baseball and found far offshore, thousands of feet below the ocean’s surface.

Here, at depths of 5km, where no sunlight can penetrate, the oxygen appears to be produced by naturally occurring metallic “nodules” which split seawater - H2O - into hydrogen and oxygen.

Among other things, the silt at the bottom of the deep sea, which will be stirred up when extracting manganese nodules, for example, is a major concern.