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A new study has revealed how phosphorus, a nutrient essential for photosynthesis, surged into ancient oceans and started Earth's first major rise in atmospheric oxygen more than 2 billion years ago.

Dr. Matthew Dodd, from UWA's School of Earth and Oceans, is lead author of the study in Nature Communications. "By fueling blooms of photosynthetic microbes, these phosphorus pulses boosted organic carbon burial and allowed oxygen to accumulate in the air, a turning point that ultimately made complex life possible," Dr. Dodd said.

The research combined a global archive of ancient carbonate rocks with modeling to simulate Earth's climate system and show that ocean phosphorus and atmospheric oxygen rose and fell together during the Great Oxidation Event.

The team measured carbonate-associated phosphate, a proxy for dissolved seawater phosphate, and found it tracked carbon isotope signals that record biological productivity and carbon burial.

Thousands of model experiments then demonstrated that transient boosts in phosphorus delivery to the oceans reproduced both rapid oxygenation and distinctive isotope fingerprints in the rock record.

"Oxygen is the hard currency of complex life and when phosphorus levels rose in the early oceans, photosynthesis revved up," Dr. Dodd said. "When more organic carbon was buried it resulted in oxygen being free to build in the atmosphere and that's how Earth took its first big breath."

The results inform creating sustainable oxygen levels on Earth as well as providing a guide for astrobiologists.

"Astronomers increasingly treat oxygen-rich atmospheres as prime targets in the search for life beyond Earth, but oxygen can, in principle, arise without biology," Dr. Dodd said. "By identifying a nutrient throttle that couples oceans, biology and the atmosphere, we offer a testable, biological pathway for creating and sustaining oxygen on living worlds.

"We also provide a framework for interpreting oxygen detections on planets outside our solar system."