How Phosphorus Kept the Air Alive

There is a question that has lingered at the edge of Earth's story for decades: after oxygen first filled the atmosphere more than two billion years ago, what kept it there? The Great Oxidation Event, as it is called, marked the moment when oxygen became a permanent feature of the air, a prerequisite for the complex life that would eventually follow. But permanence is not the same as stability, and the mechanisms that prevented oxygen from fading back into the chemical background have remained incompletely understood. Now, a study from the University of California, Riverside has identified a self-sustaining cycle that hinged on an element rarely discussed outside biology and agriculture: phosphorus .

The research, published in Nature Communications, focuses on the aftermath of the Great Oxidation Event, which occurred approximately 2.3 billion years ago . As oxygen accumulated, it reacted with minerals in the ocean, and sulfate concentrations rose. Microbes used this sulfate to break down organic matter more efficiently, a process that released phosphorus from the sediments back into seawater . That phosphorus, in turn, fueled new biological productivity. More life meant more organic carbon was buried in ocean sediments, and buried carbon could not react with oxygen to consume it. The result was a feedback loop: oxygen led to sulfate, sulfate led to phosphorus, phosphorus led to life, and life led to more oxygen .

The key to demonstrating this cycle lay in a new analytical technique. Previous methods could measure only the total amount of phosphorus preserved in ancient rocks, leaving unclear how much had been biologically available . The Riverside team, working with collaborators, developed a method that separates phosphorus based on the minerals it is bound to, dissolving each type sequentially. This allowed them to distinguish phosphorus that ancient organisms could have used from phosphorus locked in minerals and inaccessible to life .

The analysis focused on ancient rocks from South Africa. The results suggested that oxygen levels after the Great Oxidation Event fluctuated more dramatically than previously believed, swinging over tens of millions of years as the phosphorus cycle responded to changing ocean chemistry . These fluctuations would have shaped the conditions under which early life evolved, and may help explain why complex, oxygen-dependent organisms took so long to emerge even after oxygen became abundant.

The implications extend beyond the distant past. Today, warming is causing parts of the ocean to lose oxygen, a process that could reduce phosphorus availability and diminish marine productivity . Understanding how oxygen, nutrients, and life interacted in Earth's early history offers a framework for thinking about the planet's future. "Earth's history shows that oxygen, nutrients, and life evolved together," said co-author Andrey Bekker. "Understanding those connections gives us a more nuanced perspective on our own planet's future and what we might look for on other planets" .

For a planet that has been habitable for most of its existence, the finding is a reminder that habitability is not a state but a process—a balance maintained by feedbacks that are neither simple nor guaranteed. The oxygen in the air we breathe is not merely a residue of ancient photosynthesis. It is the product of a cycle, one that phosphorus helped keep turning.

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Sources:

· Nature Communications · University of California, Riverside · Naukatv.ru · Moyа Planeta