The Earth's internal heat primarily comes from three main sources:
Primordial heat: This heat is a remnant from the formation of the Earth around 4.6 billion years ago. During the accretion of our planet from cosmic dust and debris, gravitational energy was converted into heat. Additionally, the decay of radioactive isotopes, such as uranium, thorium, and potassium, present in the Earth's crust and mantle also contributes to this primordial heat.
Radiogenic heat: As mentioned earlier, certain isotopes present in the Earth's rocks and minerals undergo radioactive decay. This decay process releases energy in the form of heat. The most significant contributors to radiogenic heat are isotopes of uranium, thorium, and potassium. The heat produced by radioactive decay is continuously generated and contributes to the Earth's overall internal heat.
Residual heat from differentiation: During the early stages of the Earth's formation, the planet experienced a process called differentiation. This involved the separation of materials based on their density, leading to the formation of distinct layers. The densest materials, such as iron and nickel, migrated towards the core, releasing heat in the process. This residual heat from the differentiation of the Earth's layers continues to contribute to the internal heat of the planet.
Collectively, these three sources of heat sustain the Earth's internal temperature. The heat is transported through conduction, convection, and the slow process of heat transfer from the Earth's core to the surface. This internal heat is responsible for a range of geological activities, including volcanic eruptions, plate tectonics, and the formation of geothermal energy resources.