Long ago, before there was an earth, the first humans lived in the sky. When one of the great chiefs' daughters got sick, and no cure was found, a wise old man advised them to dig up the roots of a certain tree to cure her. A great hole was dug around the tree, but eventually it became so large that both the tree and the chief's daughter fell through into the world below.
In the world below there was a large sea on which two swans swam. As the tree and the girl fell into the sea, thunder sounded, which brought the swans to see what had happened. They found the girl drowning and so went to save her. The swans were confused because these events were so strange to them, so they went to the Great Turtle (the wisest of creatures) for advice.
The Great Turtle told the swans that the girl and the tree were a good omen. Then he ordered all his creatures to search for the tree and bring back a bit of the soil attached to its roots, so that an island for the girl could be created. The only one successful was a small toad, who came back up and spit the soil on to the top of the water, and then died. The soil turned into a large land mass and the girl then lived on it. She complained to the Great Turtle that it was dark, and that where she came from there was light. So the Great Turtle told the animals that could dig to make great holes in the sky through which light could shine.
The girl had somehow been impregnated, either when she fell into the sea or when the island had been created. Either way, her becoming impregnated was the result of sea and land coming together. In this way, the girl became the mother of all humans.