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

With higher CO (sub 2) levels, Precambrian sea-water was more supersaturated with respect to CaCO (sub 3) than Phanerozoic sea- water 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 aCO (sub 2) of sea-water. Changes in global climate (icehouse to greenhouse) and increased plate tectonic activity resulted in major changes in oceanic circulation and nutrient levels, a rise in global T and the formation of extensive shallow seas.