a revelation of logic

The other day as I stood over my teapot watching it start to boil it suddenly hit me: the reason why things boil - as in bubbles come up from inside the liquid - is that the molecules, not just on the top, but also those down underneath the surface, are turning to gas. I think the revelation began actually with the question of 'where do the bubbles come from? how does the air get down underneath? That's impossible.' (puzzled look) And then I realized, that of course the 'air' had to be the gaseous form of the water, in which case it makes sense that the bubbls would form inside because it's not just the top of the water that's getting hot enough to evaporate - duh! I'm not sure why I never connected this before, it seems quite obvious now, but somwhow I guess I just took it for granted- thought of it from a child's perspecive which is simply that 'when things get hot they bubble, and we call that boilding.' Normally I really like to know how and why things work the way the do, but I never stoped to think about this one before.