Proterozoic Sulfur Cycle : The Rise of Oxygen

Introduction According to Anbar & Knoll (2002), the Proterozoic ocean was in a transition stage from euxinic with oxygenated shallow water to the fully oxygenated water column of the present day. Though there is no direct proxy for the concentration of oxygen in the past, carbon and sulfur isotopes help constrain these concentrations. The carbon and sulfur cycles underwent vast transitions in the Proterozoic as the concentration of oxygen rose. There is evidence for two main episodes of oxygenation in the Proterozoic eon, one around 2400-2300 Ma and one in the Neoproterozoic. This second rise likely allowed the oxidative section of the sulfur cycle to become significant and the culmination of this oxygen rise may have led to the rapid diversification of animals in the Cambrian.