system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: (literally asked by my 5yo) What is coal?

I had trouble giving a concise answer, so I told her I'd ask my friends on the Internet.
gpt
......

coal used to be leaves and sticks (and animal bones if she thinks that kind of thing is cool, if it would freak her out, you can leave it out)  from a long time ago.  they fell on the ground in a forest or in a puddle just like stuff falls down today and makes a layer.  

but usually when stuff falls down, it can turn into soil (dirt) or can get burned, have you ever burned a stick in a fire?  so like that.  but this stuff from long ago got buried up or covered with water so fast, it couldn't burn or turn into dirt.  

it just kept getting buried under more and more stuff, and squashed down more and more, until it stopped being fluffy and got harder and harder.  just like how you can squash down cotton candy.  and eventually it turned into a rock.  but you can still burn that rock, and sometimes people do dig it up and burn it. 

but when they do all the stuff that happens from digging and burning can happen.