Figure: Three-stage oxidation of the Earth’s atmosphere and oceans, and co-evolution with Life

The oxidation of Earth’s surface plays a critical environmental role for the origin, evolution, and flourishing of life, as well as for the formation of sedimentary mineral and hydrocarbon resources. Yet, fundamental questions remain: when and how did the atmosphere transition from an early anoxic state to the modern well-oxygenated condition? How did interactions between the atmosphere and oceans shape Earth’s habitability over time? These questions have long remained unresolved due to the lack of reliable constraints on past atmospheric oxygen levels.

Supported by the National Natural Science Foundation of China (Grant Nos. 42425002, 42488201 and others), the teams led by Prof. Chao Li at Chengdu University of Technology and Prof. Huiming Bao at Nanjing University have pioneered the use of triple oxygen isotopes (Δ′¹⁷O) in widely accessible carbonate-associated sulfate as a tracer of atmospheric oxygen evolution, which has led to a breakthrough advance in understanding Earth’s surface oxidation history. By systematically sampling, analyzing, and integrating literature data, they established, for the first time, a high-resolution record of sedimentary sulfate triple oxygen isotopes spanning nearly 3 billion years. Using such most-direct proxy of atmospheric O₂ levels so far, the research revealed that Earth’s surface followed a three-stage oxidation history: Stage I, O₂-free atmosphere before 2.4 billion years ago; Stage II, generally low, fluctuating O₂ levels with step increases from 2.4 to 0.41 billion years ago; Stage III, stable O₂-rich atmosphere after 0.41 billion years ago, reaching modern-like levels.

This framework supports a 2-billion-year progressive, dynamic oxidation history and revealed, for the first time, a short-term (million year) negative coupling between atmospheric and oceanic O₂ levels, superimposed on a long-term (billion year) positive coupling. By establishing a direct geological record of the 2-billion-year transitional oxidation of the Earth’s atmosphere and oceans, this study provides essential environmental context for understanding the origin and evolution of life, as well as the formation of sedimentary mineral and hydrocarbon resources.

This study has been published in Nature on August 27, 2025, with the title “Two-billion-year transitional oxygenation of the Earth’s surface.” The paper’s first author is Dr. Haiyang Wang (Chengdu University of Technology), and the corresponding authors are Prof. Chao Li (Chengdu University of Technology) and Prof. Yongbo Peng (Nanjing University).