Where does the heat come from that drives mantle convection and plate motion?

Plate tectonics is the scientific theory that explains the movement of Earth's lithosphere, which is broken into several large and small tectonic plates. These plates float on the semi-fluid asthenosphere beneath them, driven by convection currents in the underlying mantle. The motion of these plates gives rise to a variety of geological phenomena, including the creation of mountain ranges, volcanic activity, and the formation of oceanic trenches. The edges where plates meet are called boundaries, and they are categorized by the way the plates interact: convergent, divergent, or transform boundaries. Each type of boundary results in different geological processes and landforms.

Radioactive decay is a crucial heat-producing process within Earth's interior. It occurs when unstable isotopes of elements like uranium, thorium, and potassium spontaneously release energy in the form of particles and heat, transforming into more stable elements. This transformation is a natural and ceaseless process that occurs in the mantle and crust. Over geologic time, the heat from radioactive decay has been a driving force in creating convection currents within the mantle. By converting atomic energy into thermal energy, radioactive decay maintains the heat necessary for keeping the mantle in a semi-fluid state, essential for the movement of the tectonic plates.

The Earth's core is a dynamic source of heat, which plays a pivotal role in plate tectonics. The core is divided into a solid inner core and a liquid outer core, both primarily composed of iron and nickel. Heat in the core is generated by two main processes: latent heat release and the heat from the crystallization of iron as it cools and solidifies. Furthermore, residual heat from the planet's formation and the frictional heating caused by the tidal forces due to the gravitational pull of the sun and moon contribute to this heat. This core heat is crucial for maintaining the thermal gradient that drives convection in the mantle.

The movement of tectonic plates is a direct result of mantle convection. As described in the step-by-step solution to the exercise, heat from the core and radioactive decay within the mantle creates buoyancy in the heated rocks, causing them to rise. Once the rock reaches the cooler upper parts of the mantle and the lithosphere, it gives off its heat, becoming denser and sinking back toward the core. This perpetual cycle creates the convection currents that act like conveyor belts for the tectonic plates. The interaction of these plates at their boundaries leads to the creation of many of Earth's surface features and is fundamentally responsible for earthquakes, volcanic activity, and mountain building.