Question: if the core of the earth is really hot why has the earth not melted?

Lidunka Vocadlo answered on 17 Jun 2015:

@james-peters pokemaster What a great question! Well the answer is that some of it has! What has happened is that the Earth used to be much hotter than it is now and, over the last 4.5 billion years, has been cooling down. As it cools, it solidifies. Now the temperature at the surface of the Earth is about zero degrees on average, and as you go down into the Earth it increases until you reach the centre which is at 6000 degrees (approximately, we don’t know exactly). The Earth’s core has an inner core (which is solid) and an outer core (which is liquid). As the Earth is cooling, the liquid outer core solidifies at the boundary between the inner and outer core – so the inner core is growing bigger, and the outer core is getting smaller. Above the outer core is the layer called the mantle – this is all solid rock, at a relatively lower temperature, and above that the solid crustal surface.