tectonic plates, increasing the geothermal gradient in the vicinity, but only the outer core is postulated to exist in a molten or fluid state, and the temperature at Earth's inner core/outer core boundary, around deep, is estimated to be 5650 ± 600 Kelvin. The heat content of Earth is 1031 joules. Much of the heat is created by decay of naturally radioactive elements. An estimated 45 to 90 percent of the heat escaping from Earth originates from radioactive decay of elements mainly located in the mantle. Gravitational potential energy, which can be further divided into: Release during the accretion of Earth. Heat released during differentiation, as abundant heavy metals (iron, nickel, copper) descended to Earth's core. Latent heat released as the liquid outer core crystallizes at the inner core boundary. Heat may be generated by tidal forces on Earth as it rotates (conservation of angular momentum). The resulting earth tides dissipate energy in Earth's interior as heat. In Earth's continental crust, the decay of natural radioactive nuclides makes a significant contribution to geothermal heat production. The continental crust is abundant in lower density minerals but also contains significant concentrations of heavier lithophilic elements such as uranium. Because of this, it holds the most concentrated global reservoir of radioactive elements found in Earth. Naturally occurring radioactive elements are enriched in the granite and basaltic rocks, especially in layers closer to Earth's surface. These high levels of radioactive elements are largely excluded from Earth's mantle due to their inability to substitute in mantle minerals and consequent enrichment in melts during mantle melting processes. The mantle is mostly made up of high density minerals with higher concentrations of elements that have relatively small atomic radii such as magnesium (Mg), titanium (Ti), and calcium (Ca). The geothermal gradient is steeper in the lithosphere than in the mantle because the mantle transports heat primarily by convection, leading to a geothermal gradient that is determined by the mantle adiabat, rather than by the conductive heat transfer processes that predominate in the lithosphere, which acts as a thermal boundary layer of the convecting mantle. Heat flow Heat flows constantly from its sources within Earth to the surface. Total heat loss from Earth is estimated at 44.2 TW (). Mean heat flow is 65 mW/m2 over continental crust and 101 mW/m2 over oceanic crust. This is 0.087 watt/square metre on average (0.03 percent of solar power absorbed by