Geology would be a lot more interesting if Emily taught it

A couple of weeks ago, we were driving home from somewhere when the following conversation took place:

Emily: Mummy, what's IN the world?
Me: What do you mean?
Emily: We're on the world, but what's inside it?
Me: Well, there is dirt, and then under the dirt is lots and lots of rock and then in the middle it is really hot and filled with liquid rock called lava.
Emily: And that's where the robots live.