We have documentary proof that the Earth/Great Turtle theory is nonsense. In "The Science of Discworld", it's shown that the Wizards of Unseen University on Discworld - which we know to be carried on the back of the Great Turtle A'Tuin and his/her attendant elephants - accidentally create our Universe. Thus by extension they also create our planet, which they christen Roundworld precisely because of their observations that everything in our Universe is balls. So that blows your theory out of the sky, I'm afraid.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'
