Scientists have helped solve a longstanding mystery about how Earth remained habitable after oxygen first accumulated in its atmosphere more than 2 billion years ago, providing evidence that an ancient ocean chemistry sustained life-friendly conditions.
The study, published in Nature Communications , was led by researchers including UC Riverside geologist Andrey Bekker. They found that changes in ancient ocean chemistry created a self-sustaining cycle that helped keep oxygen levels high after they first rose. The cycle depended on phosphorus recycling, which fueled biological productivity and helped maintain oxygen in the atmosphere.
Scientists have long known that oxygen became a permanent part of Earth's atmosphere about 2.3 billion years ago during the Great Oxidation Event. Less clear was how oxygen levels then remained high enough over millions of years to support increasingly complex forms of life.
"Living things cannot grow or function properly without phosphorus," Bekker said. "Once more of it became available in the oceans, it allowed more organic carbon to be buried. A side effect of that process is that more oxygen continued to be released into the atmosphere."
The researchers found that as oxygen entered Earth's oceans, sulfate concentrations also increased. Microbes used the sulfate to break down organic matter more efficiently, releasing phosphorus back into seawater, where it fueled new biological growth. More life meant more organic carbon was buried, allowing additional oxygen to accumulate in the atmosphere and reinforcing the cycle.
To test this idea, Bekker and collaborators analyzed ancient rocks from South Africa using a new technique that separates phosphorus based on different types of minerals it is attached to. By dissolving each type of mineral one at a time, the technique shows the researchers whether the phosphorus was available for biological functions or was tied to minerals that made it unavailable for living systems.
Until now, scientists could measure only the total amount of phosphorus preserved in rocks, making it difficult to determine how much had actually been available to support life in ancient oceans.
"We can now separate the phosphorus that was available to organisms from phosphorus that was essentially locked away," Bekker said. "That gives us a much clearer picture of nutrient levels in ancient oceans than we had before."
The findings also suggest oxygen levels fluctuated more dramatically after the Great Oxidation Event than scientists once believed. Those swings likely reshaped ocean chemistry over tens of millions of years and influenced how nutrients cycled through the environment.
The research could also reshape ideas about the evolution of early life. If oxygen remained abundant for extended periods, Bekker said, then other environmental or biological factors, not just a severely limited amount of oxygen, may have slowed the emergence of more complex organisms.
Today, climate change is causing parts of the ocean to lose oxygen. If that trend continues, phosphorus could once again become less available, reducing marine productivity and making marine ecosystems less resilient.
Insights from this research could also aid the search for life beyond Earth. Understanding how oxygen, nutrients, and life evolved together on our planet may help scientists recognize similar conditions on ocean-bearing worlds elsewhere in the universe.
"Earth's history shows that oxygen, nutrients, and life evolved together," Bekker said. "Understanding those connections gives us a more nuanced perspective on our own planet's future and what we might look for on other planets."
Nature Communications
A nutrient control on oxygenation dynamics during Earth’s Great Oxidation Episode
27-Aug-2026