What is the primary reason for the extreme heat of Earth's core?

The primary reason for the extreme heat of Earth's core is due to radioactive decay. Within the Earth, certain isotopes, such as uranium-238 and thorium-232, undergo radioactive decay, a process that releases substantial amounts of heat over prolonged periods. This heat contributes to the high temperatures found in the core, which can reach upwards of 5,000 degrees Celsius.

As radioactive materials decay, they convert their potential energy into thermal energy, which keeps the core in a molten state and supports processes such as mantle convection and plate tectonics. This continuous release of heat from radioactive decay is a significant factor in maintaining the core's extreme temperatures.

Other processes, while they may contribute to heat generation in the Earth, are not the primary reasons for the extreme heat found in the core. For instance, friction from tectonic plate movement can contribute to heat but on a much smaller scale compared to the heat produced from radioactive decay. Gravitational compression does occur as the Earth formed, contributing to initial heat, but it is not a continuous source of heat like radioactive decay. Solar radiation absorption, on the other hand, affects the Earth's surface much more directly and does not significantly influence the temperature of the core.