They are not the same. If a child says "I'm going to get an alligator and put a hat on it and fly to Antarctica!" you might say "what on earth are you talking about?" to show that you don't know about this crazy plan. It is a gentle way to say "what are you talking about?" and to show that the "what" is very unusual. If an adult says "I'm going to borrow your car keys and drive to your ex-boyfriend's party" and you respond "what the hell are you talking about? There's no chance I'm lending you my keys!" you are showing that you're disagreeing with the person agressively by adding "the hell".

Hello Sally, In both cases they is a rejection , a denial or a wonder about a statement. The difference is that " on earth" is used to rather ridicule something you heard or to wonder about it while " the hell" is expressing rejection mixed with anger and strong disapproval.

Both means the same thing, but usually using "What the hell.." shows more anger than "What on earth..". You can even take it up a notch if you are even more angry, by adding in real curse words. What the f**k are you talking about!? Which is what "wtf" stands for if you see that online.

I would avoid saying "what the hell" because it's considered cursing, so it's always going to be harsh and rude. Try not get in the habit of bad words!! But it does mean the same thing, it's just different phrasing. adding things like "what in the world", "what the hell", "what on earth" are just more exclamatory than if it was just "what are you talking about"

the hell and on earth are the phrases which you use when you are angry with someone. You just add them to a sentence and they have not different meanings.