Right at the center of our planet, about 4,000 miles below your feet, sits a giant ball of iron about the size of the Moon. The temperature there is around 5,500°C - almost exactly the temperature of the surface of the Sun. And yet, despite all that heat, the inner core is solid metal.
It seems like that shouldn’t be possible. Iron normally melts at about 1,538°C. But the pressure at Earth’s center is so unbelievably high - over 3 million times atmospheric pressure - that the iron atoms get squished into a solid arrangement and stay there. It’s pressure-frozen, not temperature-frozen.
Around that solid inner core is an outer core of liquid iron and nickel, about 1,400 miles thick. The slow churning of that liquid metal generates electric currents, which produce Earth’s magnetic field - the same field that makes a compass needle point north, and that protects the planet from a lot of cosmic radiation. So in a very real sense, the same boiling sun-hot metal at our core that gives us heat from below also gives us the magnetic shield that helps make life possible at the surface.
