V. Rama Murthy, from the University of Minnesota, and his colleagues developed high-pressure simulations and calculated a core potassium-40 content of between 60 and 130 ppm, which produces between 0.4 and 0.8 TW of heat. Estimates of the core-mantle boundary heat flux are between 8 and 10 TW, so the heat produced by potassium-40 could significantly contribute to the heat flux at the boundary. His efforts are detailed in Nature. “We now plan to expand these measurements to much higher pressures and temperatures,” Murthy said. “We shall also extend the experiments to the other major radioactive heat sources in the Earth, uranium and thorium.”