How Hot Is the Center of the Earth?

Earth's inner core reaches approximately 10,800°F (about 6,000°C) — almost exactly the same temperature as the surface of the sun. The comparison is striking: there's an area the size of Pluto sitting 3,960 miles beneath your feet that's as hot as a star. And yet the iron there is solid, not liquid, because the pressure is so immense it forces the metal to stay crystalline.

The Structure of Earth's Interior

Earth isn't uniformly hot from surface to center. It's layered, and each layer has its own temperature profile:

• Crust (0–25 miles deep): Cool at the surface, rising to about 1,600°F at the base. This is the thin shell you live on — only 1% of Earth's volume.
• Mantle (25–1,800 miles): Temperatures rise from about 1,600°F near the top to 7,200°F near the bottom. The mantle is mostly solid rock that flows extremely slowly — like a very stiff fluid over millions of years.
• Outer core (1,800–3,200 miles): Liquid iron-nickel alloy, around 7,200–9,000°F. The movement of this liquid metal generates Earth's magnetic field.
• Inner core (3,200–3,960 miles): Solid iron at roughly 9,000–10,800°F. Paradoxically solid despite the heat because of enormous pressure — about 3.6 million atmospheres.

How Do Scientists Know This?

Nobody has drilled anywhere close to the core — the deepest hole ever drilled (the Kola Superdeep Borehole in Russia) only reached 7.6 miles before heat and pressure stopped it. So how do geologists know the core's temperature?

The answer is seismology. Earthquakes send shockwaves through Earth, and the way those waves refract and reflect as they pass through different materials reveals the density and state of each layer. Laboratory experiments that replicate core pressures using diamond anvil cells help calibrate what those seismic signatures mean in terms of temperature.

The Kola Superdeep Borehole, drilled in the Soviet Union between 1970 and 1994, reached 40,230 feet — just 0.2% of the way to Earth's core. Temperatures at the bottom were already 356°F, far hotter than predicted.

Where Does All That Heat Come From?

Two main sources: primordial heat and radioactive decay.

Primordial heat is leftover energy from Earth's formation 4.5 billion years ago. When dust and rock collided and compressed to form the planet, the gravitational energy converted to heat — and the planet has been slowly radiating it ever since. This process takes billions of years to cool down significantly.

Radioactive decay accounts for roughly half of Earth's current heat output. Elements like uranium, thorium, and potassium-40 decay inside the mantle and core, releasing energy continuously. This keeps the planet warmer than it would otherwise be at this stage of its life.

What That Heat Does for Life on the Surface

The core's heat drives convection in the outer core, which generates Earth's magnetic field. Without that field, solar wind would strip away our atmosphere — the same thing that likely happened to Mars after its core cooled and its magnetic field died. Earth's heat engine is, in a very real sense, why life is possible on the surface at all.

The mantle's slow heat-driven movement also drives plate tectonics — the mechanism behind earthquakes, volcanoes, and mountain-building. The planet's surface is actively recycled by the interior's heat over hundreds of millions of years.

To see what happens when that heat escapes violently, Volcano Simulator and Earthquake Simulator demonstrate two of the main surface expressions of interior heat. Center of Earth lets you visualize the journey from surface to core. And Earth in a Day compresses billions of years of geological history into a more digestible timeframe.

For more context on how long this process has been running, how old is the Earth covers the timeline. And for what happens when the heat escapes in a particularly dramatic way, how do volcanoes create islands shows the constructive side of all that energy.