For tens of millions of years, Earth has maintained conditions hospitable to life not by accident, but through an intricate geological feedback loop only now coming into focus. Researchers publishing in the Proceedings of the National Academy of Sciences have traced a chain of causation linking sea level fluctuations to phosphate availability in the ocean, and from there to how much carbon gets buried in seafloor sediments — effectively a planetary thermostat regulating atmospheric carbon dioxide across deep time. The discovery, grounded in 60 million years of geological evidence, reframes the