The Precambrian–Cambrian boundary: seawater chemistry, ocean circulation and nutrient supply in metazoan evolution, extinction and biomineralization

This paper reviews the evidence for changes in the global environment from the late Precambrian into the Cambrian, against which the evolution of many metazoan groups and the development of biomineralization should be seen. With higher carbon dioxide levels, Precambrian seawater was more supersaturated with respect to CaCO₃ than Phanerozoic seawater and carbonates were precipitated easily. From the late Precambrian to the early Cambrian, there was a decrease in the Mg/Ca ratio and an increase in the aCO₂ of seawater. Changes in global climate (icehouse to greenhouse) and increased plate tectonic activity resulted in major changes in ocean circulation and nutrient levels, a rise in global temperature, and the formation of extensive shallow seas. The Vendian-Cambrian radiation events and onset of biomineralization must have been strongly influenced, if not driven, by these global environmental changes.