“…However, the overwhelming depletion of Mn in ca . 1.9 Ga paleosols implies that: (a) Bacterial populations capable of oxidizing Mn were too low in continental weathering environments at that time, (b) atmospheric oxygen levels were too low to make the process efficient, or (c) atmospheric oxygen levels were too low to support abiotic production of Mn oxides (Babechuk & Kamber, ; Babechuk et al., ; Diem & Stumm, ; Gall, ; Panahi, Young, & Rainbird, ; Rybacki, Kump, Hanski, & Melezhik, ; Zbinden, Holland, Feakes, & Dobos, ).…”