The Earth’s core holds immense heat, with temperatures reaching approximately 5,700 to 6,000 degrees Celsius. This extreme heat is comparable to, or even slightly hotter than, the Sun’s surface (5,500 to 5,800 degrees Celsius). The core’s sustained high temperature results from powerful processes active since Earth’s formation.
The Earth’s Fiery Birth
Earth’s initial heat originated from its violent formation billions of years ago. As the early solar system coalesced, planetesimals repeatedly collided. These high-speed impacts converted kinetic energy into thermal energy, causing the early Earth to become largely molten.
Gravitational compression further contributed to this primordial heat. As the proto-Earth grew, its increasing gravitational pull compressed material towards the center. This compression converted gravitational potential energy into heat, significantly raising the internal temperature. Residual heat from these processes still accounts for a portion of Earth’s internal heat.
Atomic Decay Inside
A primary source of Earth’s ongoing internal heat is radioactive decay. Unstable isotopes like Uranium-238 (²³⁸U), Uranium-235 (²³⁵U), Thorium-232 (²³²Th), and Potassium-40 (⁴⁰K) are present throughout Earth’s mantle and crust. These isotopes continuously break down into more stable elements, releasing thermal energy.
This continuous decay substantially contributes to the planet’s heat, accounting for approximately 50% of the total internal heat output. Scientists estimate this radiogenic heat contributes around 20 terawatts from uranium and thorium decay chains alone. This constant energy release sustains high temperatures within Earth’s deep interior over vast geological timescales.
Heat’s Journey Outward
Heat generated within Earth’s core and lower mantle steadily moves outward through convection. In the outer core, where molten iron exists, this heat drives the movement of the liquid metal. These convection currents create Earth’s magnetic field.
In the mantle, heat transfers through slow, continuous convection of solid rock. Hotter, less dense material slowly rises, while cooler, denser material sinks, forming vast convective cells. This mantle convection drives plate tectonics, constantly reshaping Earth’s surface as heat escapes from the interior.
Probing Earth’s Depths
Direct observation of Earth’s deep interior is impossible, so scientists use indirect methods to understand its hot, dynamic nature. The primary technique involves studying seismic waves from earthquakes. Their travel through Earth’s layers provides crucial insights.
There are two main types of seismic waves: P-waves (primary waves) and S-waves (secondary waves). P-waves travel through both solid and liquid materials, while S-waves only propagate through solids. By analyzing how these waves travel, refract, or reflect, researchers deduce the physical properties of materials they pass through. For instance, S-waves not passing through the outer core indicates its liquid state, while P-wave behavior supports a solid inner core, both at extremely high temperatures and pressures.