The reaction "igneous rocks plus acid volatiles to give sedimentary rocks plus seawater" has long been the basis for geochemical balance calculations, and also the basis for chemical arguments for the constancy of seawater composition. In most balance calculations based on continental igneous rocks as the sediment source, there is an unaccounted excess of iron and calcium in the sediments. This excess may well have come from submarine alteration of mafic volcanic rocks, a process shown to be important today by recent dredging and coring, and probably of greater relative importance in early earth history. Both subaerial and submarine weathering contribute to the mass of cycling sedimentary rocks and hence to oceanic composition.

The submarine alteration branch of the sedimentary geochemical balance may be written: mafic volcanics + volatiles = greenstones + cherty iron formations + carbonate rocks. No major differences in oceanic composition have been deduced as stemming from early greater relative submarine alteration, but the sedimentary mass is predicted to have been richer than now in carbonate rocks, chert, and iron minerals. Most of the early carbonate rocks, because of selective cycling, now exist as Phanerozoic deposits.

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