Constraints on Paleoproterozoic atmospheric oxygen levels

The oxygenation of Earth’s surface environment dramatically altered key biological and geochemical cycles and ultimately ushered in the rise of an ecologically diverse biosphere. However, atmospheric oxygen partial pressures (pO₂) estimates for large swaths of the Precambrian remain intensely debate...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2018-08, Vol.115 (32), p.8104-8109
Main Authors: Bellefroid, Eric J., Hood, Ashleigh v. S., Hoffman, Paul F., Thomas, Matthew D., Reinhard, Christopher T., Planavsky, Noah J.
Format: Article
Language:English
Subjects:
Anomalies
Atmospheric chemistry
Biological Sciences
Biosphere
Carbonates
Cerium
Cerium oxides
Constraint modelling
Earth surface
Geochemical cycles
Low concentrations
Oxidation
Oxygen
Oxygenation
Physical Sciences
Precambrian
Precipitates
Sedimentology
Stratigraphy
Trace elements
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Summary:The oxygenation of Earth’s surface environment dramatically altered key biological and geochemical cycles and ultimately ushered in the rise of an ecologically diverse biosphere. However, atmospheric oxygen partial pressures (pO₂) estimates for large swaths of the Precambrian remain intensely debated. Here we evaluate and explore the use of carbonate cerium(Ce) anomalies (Ce/Ce*) as a quantitative atmospheric pO₂ proxy and provide estimates of Proterozoic pO₂ using marine carbonates from a unique Precambrian carbonate succession—the Paleoproterozoic Pethei Group. In contrast to most previous work, wemeasure Ce/Ce* on marine carbonate precipitates that formed in situ across a depth gradient, building on previous detailed sedimentology and stratigraphy to constrain the paleo-depth of each sample. Measuring Ce/Ce* across a full platform to basin depth gradient, we found only minor depleted Ce anomalies restricted to the platform and upper slope facies. We combine these results with a Ce oxidation model to provide a quantitative constraint on atmospheric pO₂ 1.87 billion years ago (Ga). Our results suggest Paleoproterozoic atmospheric oxygen concentrations were low, near 0.1% of the present atmospheric level. This work provides another crucial line of empirical evidence that atmospheric oxygen levels returned to low concentrations following the Lomagundi Event, and remained low enough for large portions of the Proterozoic to have impacted the ecology of the earliest complex organisms.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1806216115