Answers are grounded in this paper and cite their sources.
The presence of organic material in some manganese-rich nodules suggests that the nodules are of biological origin. This suggestion leads to the proposal that in sea water, heavy metals get protection from hydrolysis by organic complexing; parts of these complexes become metabolized, the remaining parts then precipitate. These processes would explain a number of interesting observations.
No takes yet. Share an insight, caveat, or question.
J. A. Graham (1959) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: