Researchers have identified a biological feedback mechanism that may explain how Earth sustained atmospheric oxygen after the Great Oxidation Event approximately 2.3 billion years ago. The international team, including geologist Andrey Bekker from the University of California, Riverside, published their findings in Nature Communications following analysis of South African rock samples.
The mechanism centers on a chemical cycle involving phosphorus, an essential nutrient for life. As oxygen entered the oceans during this ancient period, it altered seawater chemistry and increased sulfate concentrations. Microbes then utilized sulfate to decompose organic material more efficiently, releasing phosphorus back into the water where other organisms could access it. This increased phosphorus availability stimulated biological productivity, allowing more organic carbon to settle on the seafloor rather than decompose. Since organic decomposition consumes oxygen, the burial of additional carbon supported continued atmospheric oxygen accumulation.
To investigate this process, scientists employed an advanced analytical technique that distinguished between phosphorus available to organisms and phosphorus locked within mineral structures. Previous research could measure total phosphorus content in ancient rocks but could not determine whether living things could actually utilize it. By selectively dissolving different mineral components, researchers separated biologically accessible phosphorus from inaccessible reserves, providing clearer insight into prehistoric nutrient cycles.
The research suggests Earth’s atmospheric oxygen history may have been more volatile than previously understood, with oxygen levels potentially rising and falling dramatically over millions of years. This finding has implications for understanding why complex organisms took considerable time to emerge after oxygen became abundant. Additionally, the study relates to contemporary ocean conditions, as current climate-driven oxygen depletion in marine environments could disrupt phosphorus recycling and harm biological productivity.
The findings may also assist scientists in evaluating potential habitability on distant planets and ocean-bearing worlds by identifying chemical relationships that could support sustained life over extended periods.
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