In Chinese mythology, Pangu is the ancestor of humanity.
In the distant past, before heaven and earth had formed, the world was nothing but a vast, dark chaos. Then Pangu emerged. Enraged by the endless darkness before him, he took a stone axe he had crafted and swung it at the chaotic void.
"With a thunderous roar, the light, clear yang qi rose and became the sky; the heavy, turbid yin qi sank and became the earth."
From that point on, Pangu stood with his head holding up the blue sky and his feet planted firmly on the earth. As the distance between heaven and earth grew ever greater, Pangu became a giant who literally propped up the heavens and pressed down the earth.
Pangu became the sole master of heaven and earth. When he was happy, the sky was clear; when he grew angry, thunder rumbled; when he wept, torrential rain poured down, gathering into rivers, lakes, and seas; and when he sighed, fierce winds swept across the land.
Countless years later, Pangu died, his body stretching across the land: his head became Mount Tai in the east, his toes became Mount Hua in the west, his belly became Mount Song in the center, his left and right shoulders became Mount Heng in the south and Mount Heng in the north, and his hair and body hair all transformed into flowers, grass, and trees.
Later, when the sky formed its dome, the myth of Nüwa mending the heavens emerged. Legend says Nüwa recreated humanity, allowing the human race to flourish and multiply through generations.
Later, the idiom "opening heaven and earth" came to describe doing something for the very first time in history.
Source: *Yiwen Leiju*
Meaning of the Idiom: Later, the Chinese idiom "开天辟地" came to describe doing something for the very first time in history.