Table 1. Summary of estimates of O₂ levels in the Archean atmosphere.

Archean O2 estimate	Global or local	Proxy	Minimum or maximum estimate	Author
PO2 < 10−6	Global	MIF-S anomalies	Maximum	(3–5)
PO2 < 10–3.8 PAL	Global	Detrital pyrite and uraninite	Maximum	(6–9)
PO2 < 10–4.7 PAL	Global	Fe mobility in paleosols	Maximum	(10–13)
PO2 > 10–6.9 PAL	Global	Mo in shales	Minimum	This study
>0.01 Tmol O2/year	Local	Mo in shales	Minimum	This study