Subject: Where does the heat from the core of the earth come from?

Why I asked?  Just wondered.  

Actually, I was meandering with my mind on how wastes such as ramen cups can be
disposed of and came across the solution that they can perhaps be thrown into a
volcano.  There must be some flaw to that idea... 

It's also something that I've always wondered.  I've also seen diagrams of other
planets, the sun, and the moon cut up on the sides like melons, exposing the
various inner layers of each heavenly body.  All of them have hot cores.  Why?

Re: Where does the heat from the core of the earth come from?