Earth's Core Is Hotter Than Sun's Surface

It's a startling comparison to consider: the very center of our own cool, rocky planet burns with more intensity than the visible face of our solar system's star. While the Sun's core is a fusion furnace reaching millions of degrees, its surface layer, the photosphere, is significantly cooler. Deep beneath our feet, the immense pressure creates conditions that allow Earth's solid iron-nickel core to reach a temperature hotter than that solar surface, making our planet's heart a truly extreme environment.

This incredible internal heat is a legacy of Earth's violent birth. A significant portion is "primordial heat," leftover energy from the gravitational collapse of matter and the constant, massive collisions that formed our planet 4.5 billion years ago. This ancient warmth is supplemented by a steady, ongoing process: the slow decay of radioactive isotopes, primarily uranium and thorium, distributed throughout the planet's mantle and core. This process acts like a vast, slow-burning nuclear reactor, continually releasing energy and keeping Earth's interior fiery hot.

The combination of this intense heat and crushing pressure, millions of times greater than at the surface, drives the engine of our planet. It keeps the outer core in a liquid, molten state, and the flow of this liquid iron is what generates Earth's protective magnetic field. In a fascinating paradox, it is also this same immense pressure that forces the even hotter inner core to remain a solid, crystalline ball of iron.