Sixty-six million years ago, Earth was a greenhouse world with no polar ice, CO2 above 800 ppm, and palm trees growing in Alaska. This episode of Fault Lines asks why all that warmth slowly disappeared over the following 50 million years of the Cenozoic era. Ola and Amara examine a University of Southampton PNAS study finding that seawater calcium dropped by more than half across that period, walking through the foram proxy method used to reconstruct the record, debating whether calcium decline drove CO2 down or simply tracked alongside it, and weighing the Drake Passage and Antarctic Circumpolar Current as competing explanations. Listeners interested in deep-time climate science will come away understanding why geochemical ocean processes, not just tectonics or ice dynamics, may be the true long-run thermostat of Earth's climate.