Answer:
It's like food but water kills it. What is it?
I never was, am always to be. No one ever saw me, nor ever will. And yet I am the confidence of all, To live and breath on this terrestrial ball.
When I'm born I fly. When I'm alive I lay. When I'm dead I run.
Power enough to smash ships and crush roofs. Yet it still must fear the sun.
Iron roof, glass walls, burns and burns and never falls.
You use it between your head and your toes, the more it works the thinner it grows.