While hydrothermal activity can produce considerable quantities of hydrogen, in porous rocks often
found under seafloors, radiolysis could produce copious amounts as well.
Among other things, GRACE may have
found a crater deep
under the Antarctic ice that may mark an asteroid impact greater than the one that doomed the dinosaurs, measured the
seafloor displacement that triggered the tsunami of 2004, and quantified changes in subsurface water in the Amazon and Congo river basins.