Triple oxygen isotope constraints on atmospheric O <sub>2</sub> and biological productivity during the mid-Proterozoic
Peng Liu, Jingjun Liu, Aoshuang Ji, Christopher T. Reinhard, Noah J. Planavsky, Dmitri Babikov, Raymond G. Najjar, James F. Kasting
Abstract
Significance Constraining the abundance of molecular oxygen (O 2 ) in Earth’s atmosphere over time is a problem of central importance for understanding the evolution of complex life. Here, we refine previous analyses of the rare oxygen isotope composition of sedimentary sulfates to develop improved estimates of atmospheric O 2 during Earth’s mid-Proterozoic era. Previous analyses of these data had predicted O 2 concentrations well below 1% present atmospheric level. Our new calculations suggest that this value is closer to a lower limit on atmospheric oxygen partial pressure unless the climate was warmed significantly by biogenic methane. The calculations also show that marine productivity cannot be reliably estimated from these data because of the slow rate of transfer of O 2 across the air–sea interface.