Before the supreme ancestors, the world (not just the earth), was just a big black ball of chaos, with no order what so ever. Inside side this chaos there was Pan Gu. He slept in this ball for 18,000 years, and woke one day. When awoken he felt unhappy with his surrounding, so he got an ax and with all his might crack the ball open. When the ball cracked all the light (the good part of the ball) floated up, making the heavens. All the cold and dark stuff stayed below making the earth. Pan Gu was in the middle his feet touched earth but his head touching heaven.