No evidence for high atmospheric oxygen levels 1,400 million years ago


Zhang et al. (1) recently proposed atmospheric oxygen levels of ∼4% present atmospheric levels (PAL) based on modeling a paleoenvironment reconstructed from trace metal and biomarker data from the 1,400 Ma Xiamaling Formation in China. Intriguingly, this pO2 level is above the threshold oxygen requirements of basal animals and clashes with evidence for atmospheric oxygen levels textlesstextless1% PAL in the mid-Proterozoic (2). However, there are fundamental problems with the inorganic and organic geochemical work presented by Zhang et al. (1). The authors infer oxic deposition of the Xiamaling Formation based principally on the predominance of low V/Al ratios relative to a modern crustal average, which they attribute to V loss from the sediment (1). However, significant variability in detrital V/Al ratios of the upper crust make small local … [↵][1]1To whom correspondence should be addressed. Email: [1]: #xref-corresp-1-1

Proceedings of the National Academy of Sciences