Emerging views on the evolution of atmospheric oxygen during the Precambrian

摘要

The oxygenation of the atmosphere produced some irreversible changes in the Earth's history, including evolution of higher biological forms. Several aspects of this important process, such as its timing and causes, have remained subjects of debate. The present review is an attempt to provide an update on issues related to the evolution of atmospheric oxygen during the Precambrian. It is generally believed that the amount of atmospheric oxygen increased during the Paleoproterozoic despite the fact that photosynthesis originated much earlier in the Earth's history. The pattern of Fe retention in paleosols and the record of mass-independent fractionation in sulfur isotopes confirm that the transition to more oxidizing conditions took place during the Paleoproterozoic. Various mechanisms, ranging from an increase in the sources of oxygen to a decrease in its sinks, have been envisaged as processes causing the oxygen rise during the Paleoproterozoic. Conventionally, it is believed that the burial of photosynthetic carbon has allowed the establishment of oxygen. However, the transition in mantle oxidation states and the escape of hydrogen during photolysis of methane of biogenic origin have also been suggested as having played an important role in the establishment of free molecular oxygen in the atmosphere-hydrosphere system. The coincidence of timing of the oxygen rise and the positive excursions in carbon isotope compositions of carbonate rocks during the Paleoproterozoic suggests an important role for the carbon cycle in atmospheric oxygen evolution. Better quantitative modeling of atmospheric oxygen levels may be essential to allow full comprehension of the timing, causes and consequences of the oxygen rise in the Earth's history. Quantitative modeling is essential as it can lead to an unraveling of the co-evolutionary nature of the surface environment and the biosphere of the Earth.