This is one of two Aztec creation stories.
Quetzalcoatl, the light one, and Tezcatlipoca, the dark one, looked down from their place in the sky and saw only water below. A gigantic goddess floated upon the waters, eating everything with her many mouths.
The two gods saw that whatever they created was eaten by this monster. They knew they must stop her, so they transformed themselves into two huge serpents and descended into the water. One of them grabbed the goddess by the arms while the other grabbed her around the legs, and before she could resist they pulled until she broke apart.
Her head and shoulders became the earth and the lower part of her body the sky.
The other gods were angry at what the two had done and decided, as compensation for her dismemberment, to allow her to provide the necessities for people to survive; so from her hair they created trees, grass, and flowers; caves, fountains, and wells from her eyes; rivers from her mouth; hills and valleys from her nose; and mountains from her shoulders.
Still the goddess was often unhappy and the people could hear her crying in the night.
They knew she wept because of her thirst for human blood, and that she would not provide food from the soil until she drank.
So the gift of human hearts is given her.
She who provides sustenance for human lives demands human lives for her own sustenance. So it has always been; so it will ever be.