Is the centre of the earth filled entirely of molten material or is there some gas?

We posed this question to Hazel Rymer from the Open University...

Hazel - Well, there's no gas right inside the centre of Earth because the pressure is much too high. It only comes out as gas when it finally gets to the surface. The magma that comes out of a volcano is really only sourced several kilometres beneath the surface. I mean, it's really just beneath the skin effectively.