Reversed marine phosphorus gradient in the Ediacaran Ocean.

The Ediacaran Period (635-539 Ma) witnessed the emergence of early animals, rapid oceanic oxygenation, and rising oceanic P availability. However, the relationships among these developments remain intensely debated. Here, we present high-resolution carbonate-associated phosphate (CAP) data from seven Ediacaran sections spanning diverse depositional environments across South China. Contrary to the modern ocean, our measurements reveal an inverted phosphorus (P) gradient, with lower P availability at depth. By integrating these data with a quantitative biogeochemical model, we show that increasing shallow-water P inputs drove enhanced productivity and bottom-water anoxia on continental shelves, while P-starved distal oceans became progressively oxygenated from the top downward, providing an oxygenated niche-a deep-ocean cradle-for early metazoan evolution. Our study establishes a conceptual framework linking nutrient dynamics, marine oxygenation, and evolutionary innovation in Earth's early history.