Two-billion-year transitional oxygenation of the Earth's surface

Area of Science:

• Geoscience
• Biogeochemistry
• Paleoclimatology

Background:

• Earth's oxygenation was a stepwise process, with details of the transition remaining unclear.
• The rise of atmospheric oxygen (O2) is crucial for understanding early life evolution.
• Previous studies lack high-resolution data on the long-term oxygenation history.

Purpose of the Study:

• To reconstruct Earth's oxygenation history using a novel proxy.
• To investigate the relationship between atmospheric O2 levels and ocean oxygenation.
• To explain Neoproterozoic carbon cycle anomalies and the rise of complex life.

Main Methods:

• Analysis of mass-independent oxygen isotopes in sedimentary sulfate (Δ'17Osulfate) over 2.5 billion years.
• Integration of existing sedimentary Δ33S data.
• Quantitative biogeochemical modeling.

Main Results:

• A 2-Gyr transition of fluctuating atmospheric partial pressure of O2 (pO2) from an O2-free state to modern levels.
• Evidence for elevated pO2 after 1.0 Ga.
• Coupled declines in Δ'17Osulfate and sulfate-δ34S during Neoproterozoic carbon isotope excursions, linked to increasing pO2.

Conclusions:

• Earth's atmosphere and oceans experienced a lengthy, dynamic co-oxygenation history.
• Episodic ocean oxygenation was driven by increased atmospheric O2 influx, with negative feedback mechanisms.
• This dynamic oxygenation provides a coherent explanation for Neoproterozoic carbon cycles and the rise of complex life.