The center of the Earth is very hot. Scientists think it is about 6,000°C. That is about as hot as the surface of the Sun! Nobody can go there. The deepest hole people have ever dug is only about 12 kilometers deep.

So scientists study earthquake waves and do experiments with diamonds. The iron in the center is very hot, but it is still solid. This is because the pressure there is very, very high.

Earth's center is about 6,400 kilometers below us, but the deepest hole humans have ever dug is only about 12 kilometers deep. So how do scientists know what is down there? They study how earthquake waves travel through the planet, and they recreate the conditions of the core in the lab.

In 2013, a French team squeezed iron between diamonds, heated it with lasers, and used X-rays to see when it melted. They estimated that the boundary of the inner core is about 6,000°C, close to the temperature of the Sun's surface. Amazingly, the inner core stays solid because the enormous pressure prevents the iron atoms from moving freely.

Although Earth's center lies about 6,400 kilometers beneath us, scientists have pieced together a detailed picture of it. In 1936, Danish seismologist Inge Lehmann noticed subtle anomalies in earthquake waves and proposed a solid inner core within the liquid outer core. Its temperature is estimated through experiments: in 2013, a French team compressed iron between diamonds to around two million atmospheres, heated it with lasers, and used X-rays to detect melting. Extrapolating to the inner core boundary, where pressure exceeds three million atmospheres, they estimated about 6,000°C, give or take 500 degrees, roughly 1,000 degrees higher than an influential earlier result and comparable to the Sun's surface.

The iron stays solid because extreme pressure raises its melting point. Part of the heat is left over from Earth's formation, while the KamLAND detector in Japan showed that about half of the heat flowing out of the planet comes from radioactive decay. This heat drives the motion of the liquid outer core, which generates the magnetic field that shields us from the solar wind. That said, the estimate relies on extrapolation, and different experiments disagree by hundreds of degrees.