 There's plenty of decay going on in the core and so the core is extremely hot. Interestingly, the geophysicist tells us that the inner core is solid and the outer core is liquid. Liquid is very different physically than solid. The outer core, this liquid outer core is really hot and it's much hotter than the mantle just above it. So the boundary between the outer core and the lower mantle is extremely different in temperature and it's more than a thousand degrees centigrade difference. That means it's not terribly stable. So others will tell you about plumes, but plumes are a reflection of the cooling and this discontinuity between the really high temperatures in the core and the much lower temperatures in the lower mantle. But the point I wanted to make as someone who thinks about patrology, igneous rocks is that this discontinuity sets up the start of a bloom so that the hot viscous mantle just above that discontinuity between the outer core and the lower mantle it sets up a bunch of material that slowly rises and it's not molten. It's solid material that's quite gooey. So it rises and as it rises and gets to lower normal pressures it starts to melt incrementally. Melts, melts, melts and it's only towards the very, very top that we see a molten material which then can come out with massive flows of salt onto the continents and ocean floors. So that's a reflection of the cooling of the earth and this incredible thermal energy that we started with and a whole bunch of radioactivity driving all of this and keeping this hot so that it's still extremely hot down there. So now this is part of the convective mantle and they calculate, they make estimates that it takes 200 million years to entirely overturn the mantle which means it's mixing and if you think about over 4.5 billion years it's been mixed thoroughly a number of times. But that doesn't mean it's all the same and there are changes. So as we go down into the earth we realized some years ago there was a reflector at 660 kilometers which was first identified by a Russian called Morović so of course we call it the moho and this is a transition from one mineral phase to another due to pressure.