Libby is a teenage girl who was Sheldon Cooper's first crush. They met in 1990.
Libby helped Sheldon gain an interest in geology by introducing him to rocks that can shine bright diverse array of colors in the dark, helping him realize that tectonic plates are what helped lead to a diversity of animals upon different continents to the point many exotic animal species are only endemic to one continent. Sheldon was intrigued by this and wanting to learn more to attack Pastor Jeff's endorsement of religion and Christianity, he joined Libby on a journey to study more rocks. Eventually Sheldon will hate geology.