This article the crux, is this about extractable hydrogen or some proxy about it (vs just "interesting number"), to the last sentence. The abstract is again th

This article the crux, is this about extractable hydrogen or some proxy about it (vs just "interesting number"), to the last sentence. The abstract is again the best summary: "[...] Given the associated uncertainty, stochastic model results predict a wide range of values for the potential in-place hydrogen resource [103 to 1010 million metric tons (Mt)] with the most probable value of ~5.6 × 106 Mt. Although most of this hydrogen is likely to be impractical to recover, a small fraction (e.g., 1 × 105 Mt) would supply the projected hydrogen needed to reach net-zero carbon emissions for ~200 years."