Thank you.

I'm confused. Are either of these processes related to the pressure of the mass above? I always thought that was what caused the heat. Two more questions. 1. Is radioactive decay triggered by something or does it just happen with those particular elements? 2. Is there something besides the insulating qualities of the crust that keep primordial heat from cooling quicker. Billions of years seems like a long time for something to cool down. I know it is a lot of mass but......