The Uranium and Actinide Cycle in the Earth's Mantle: Implications for the Thermal and Geophysical Dynamics of the Planet

The conventional paradigm of planetary geodynamics models the Earth’s mantle as a passive thermal engine driven by secular cooling and distributed radiogenic decay, assuming that long-lived radioactive elements (, , , and ) were largely depleted from the deep mantle and concentrated in the continental crust during early planetary differentiation. However, this framework struggles to reconcile persistent global anomalies, notably the approximately 20 TW thermal deficit in Earth's heat flow budget. To address these limitations, this paper proposes an alternative model: the Basal Geothermal Engine operating at the core-mantle boundary (CMB), specifically within the layer and Ultra-Low Velocity Zones (ULVZs). Incorporating mantle convection as a continuous conveyor belt combined with the action of Pluton-Surfactants (TAPs), heavy actinide-bearing oxides () are systematically recycled and gravitationally segregated toward the deep mantle floor rather than being permanently evacuated. Under the extreme temperatures () and megabar pressures of the CMB, these refractory oxides undergo direct thermal dissociation into dense liquid metallic uranium. Furthermore, high-pressure neutron physics demonstrates that extreme volumetric compression drastically reduces the critical mass (), enabling basal reservoirs to transition from slow, stationary thermal reactors into cyclic, high-reactivity systems. We formalize this catastrophic transition through the NESIR (Nuclear Explosion Sudden Internal Release) mechanism, wherein geometrical compaction and critical thresholds trigger rapid supercritical pulses. These deep-seated energetic releases propagate catastrophic shockwaves through the lithosphere, accounting for progressive seismite sequences, the structural fracturing of submarine and continental anticlines, massive hydrocarbon venting, and the primary triggers of major mass extinction events throughout Earth's geological history.