Why do people scream?

I just cant see any point in screaming, I mean if a lion is around and you suddenly scream about it then wham it instantly knows your there and kills you so bad idea screaming there. If there's an earthquake and people scream dose that stop the earthquake? no it doesn't so what the fck is the point in humans screaming. I really cant see why humans scream it serves absolutely no purpose and could even get you killed if there is a predator about so what is the point ?