The trigger for biomineralization of metazoans in the terminal Ediacaran, ~550 million years (Ma) ago has been suggested to be the rise of oxygenation or an increase in sea water Ca concentration, but geochemical and fossil data have not been fully integrated to demonstrate cause and effect. Here we combine the record of macrofossils with early marine carbonate cement distribution within a relative depth framework for terminal Ediacaran to Cambrian successions on the eastern Siberian Platform, Russia to interrogate the evolution of sea water chemistry and biotic response. Prior to ~545 Ma the presence of early marine ferroan dolomite cement suggests dominantly ferruginous anoxic ‘aragonite-dolomite seas’, with a very shallow oxic chemocline that supported mainly soft-bodied macrobiota. After ~545 Ma, marine cements changed to aragonite/high-Mg calcite, and this coincides with the appearance of widespread aragonite and high-Mg calcite skeletal metazoans suggesting a profound change in sea water chemistry to ‘aragonite seas’ with a deeper chemocline. By early Cambrian Stage 3, the first marine low-Mg calcite cements appear coincident with the first low-Mg calcite metazoan skeletons suggesting a further shift to ‘calcite seas’. We suggest that this evolution of sea water chemistry was caused by enhanced continental denudation that increased the input of Ca into oceans so progressively lowering Mg/Ca which, combined with more widespread oxic conditions, facilitated the rise of skeletal animals and in turn influenced the evolution of skeletal mineralogy.