Science Questions

Why hasn't the earth's core cooled down yet?

The Earth's core is basically molten and the Earth is in the region of four billion or so years old. How come it hasn't cooled down over the last four and a half billion years, and why hasn't man tried to tap into all that energy? Andy on the A120

We have tried to tap into that energy. Iceland is one of the biggest banana producers in the world, and the reason is that they use this geothermal energy. Iceland has a lot of hot magma near the surface, and so they use that heat to do all sorts of things. There are other places around the world where they use this heat in the hot Earth around them to heat water and power things. But the ultimate question of where does that heat come from, is that the heat has, to a certain extent, always been there. The Earth is a huge body, and as a result, it has a huge amount of energy trapped under its surface, but it has cooled down. When the Earth was first formed, it was essentially a blob of molten material in space. Since that time it has cooled a lot, but because we're quite a big planet, we haven't lost all our heat yet. Then there's a second contribution. In the early days of the Earth when it was still molten, all the heavy and dense elements sunk deeper into the Earth's crust than the lighter ones. The heavy dense things were the ones that might be radioactive and for a while, people were suggesting that there might be a big geo-reactor under the Earth. This is a giant natural nuclear reactor and when you get critical masses of the right materials in the right place at the right time, they can begin their own chain reaction. That produces heat and we think that that might be contributing to heating the Earth up.

October 2006