She wondered how to give a moon to Her dear earth. it wouldn't do to simply give her a comet to be captured by her gravity. then She saw that one of her sisters—theia was her name—shared her orbit. "she will do nicely," She thought to herself, and with Her magic did She disturb theia's orbit, and sent her onto a collision course with earth.
eventually, they were so close that they could feel each other's gravity, and they started falling into each other. "hello, dear sister," they said to each other. soon they were so close that their atmospheres could touch.
and then, finally, they embraced.
they smashed into each other, penetrating deep, leaving pretty scars in earth's lower mantle. they shattered out of each other, debris falling into orbit around them and forming a ring. they melted into one another, liquid rock mixing together, hot with love.
they became one. theia now a part of her forever.
and soon enough, the ring of debris formed into another.