# Eli5: why isn’t the earth core melting? If I understand correctly it is made out of iron and nickel and it floats in a molten bath of iron and nickel.

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Eli5: why isn’t the earth core melting? If I understand correctly it is made out of iron and nickel and it floats in a molten bath of iron and nickel.

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Pressure – there’s so much pressure from the entire rest of the Earth pressing down on the solid core that it stays solid despite its temperature being high enough for it to be liquid if it were at the Earth’s surface. Whether a substance is liquid, solid or gaseous depends on both temperature and pressure (for most things). Raise the pressure, and the melting point gets higher.

Everything consists of atoms, and the main difference between gas, liquid, and solid is how much those atoms can move. In a liquid, they can move past one another, which we experience as fluid. In some things, like syrup, they can still move past eachother, but it’s more difficult, so while still fluid it acts different than water. Finally, when they can’t really move past eachother, you get a solid.

There are really two ways to influence how much atoms can move:

Temperature increases the energy atoms have to move. Melting something is basically just giving it’s atoms energy until they have enough to push “free” from its current position.

Pressure is the space atoms have to move around. If there is not enough space, they can’t really move as much as they normally would with their current energy. This means you would have to increase the temperature even more so it can push harder.

The Earth is basically a sandwich; a solid outer shell, a liquid middle, and a solid core. The shell is solid, because it is not hot enough to melt. The middle is liquid, because it is extremely hot. Then we get the core: also extremely hot, but it has an entire planet pushing down into it, making it also have an extreme amount of pressure. This pressure is enough to increase its melting point to past its current temperature, and makes it a solid.