Fig. 7
From: Highly fractionated chromium isotopes in Mesoproterozoic-aged shales and atmospheric oxygen
Oxygen model results. Results are redrawn from ref.8 including interpolated results for oxygen levels of 10−2 PAL and 10−4 PAL, not presented in the original figure. The x axis presents soil water residence time, and the blue bar on top represents the range in modern soils. The y axis represents the fraction of the original Cr(III) in the soil oxidized to Cr(VI) and the contours represent different levels of atmospheric oxygen in fraction of PAL. The lower-limit range of oxygen requirements for bilaterian animals with a simple circulatory system64 is constrained between the green lines. The lower red circle represents the maximum atmospheric oxygen concentration as constrained by Planavsky et al.8, whereas the upper red circle represents the minimum atmospheric oxygen estimate of the present study
