Long ago the entire universe was in an egg shape cloud.
Lighter Pure Elements
Heavier Impure Elements
Over 18,000 years a huge giant called Pan Gu grow inside it.
On the day he awoke he stretched and the egg broke releasing the matter of the universe.
The lighter pure elements drifted up to create the sky and heavens and the heavier impure element settled to make the earth.
To keep the heavens an the earths separated Pan Gu held them apart with his body. When they were set in place Pan Gu died.
After death his arms and legs became the four direction and the mountains. His blood became the rivers. His left eye became the sun and his right eye became the moon. All the rest of his body part formed the world to how it is today.