Abstract: The fuel driving plate tectonics, volcanoes, mantle convection, and the Earth's magnetic field comes from two sources: primordial energy from assembling the planet and nuclear energy from the heat produced during natural radioactive decay. Various models with widely varying estimates have been proposed as to how much primordial and nuclear fuel remains inside Earth. However, teams of geologists and neutrino physicists are boldly claiming that the new field of Neutrino Geophysics can determine how much nuclear fuel (i.e., radioactive power) remains in the Earth's tank. For the last two decades neutrino physicists have been detecting low energy (MeV) electron anti-neutrino being emitted from the Earth (geoneutrinos), produced via beta minus radioactive decay of U and Th. Collectively, the flux of geoneutrinos measured at detectors in Japan and Italy, soon a report from Canada, and in 2026 data from China reveal the radiogenic power driving the Earth's engine. These data will define the compositional model of the Earth, place tight constraints on its thermal evolution, and independently confirm the planets chondritic ratio of refractory elements.