Ancient South African Rocks Point to a Phosphorus Cycle That Kept Oxygen in Earth’s Air
A new study of ancient South African rocks suggests that phosphorus recycling in the oceans helped keep oxygen levels high after the Great Oxidation Event about 2.3 billion years ago. As oxygen rose, sulfate increased and microbes broke down organic matter more efficiently, releasing phosphorus that fueled more biological growth. The resulting burial of organic carbon reduced oxygen consumption, allowing the atmosphere to retain more of the gas.
The research centers on rocks from South Africa and a chemical method that releases phosphorus from different minerals sequentially. This lets scientists tell whether ancient phosphorus was biologically usable or bound in unavailable forms, a distinction earlier total-phosphorus measurements could not make.
The proposed feedback loop links rising oxygen to higher sulfate, more efficient microbial decomposition, and phosphorus release. That nutrient supported more growth; when resulting organic carbon was buried, less oxygen was consumed. The study also suggests oxygen after the Great Oxidation Event did not stabilize immediately, but fluctuated across tens of millions of years.
This finding may shape how researchers and science communicators interpret early Earth habitability and nutrient cycling. It could influence future studies of ocean chemistry and oxygen persistence, potentially informing how scientists assess conditions for complex life on other planets. For the public, it may deepen understanding of how biological and geological systems interact over vast timescales, though direct near-term societal effects are likely limited.