Because of it's size it is either for a child or for pure decorative purpose.
"During the Middle Ages in Europe male earrings alternated between being popular and being out of style for long periods of time until in the 13th century when the Catholic Church forbade the piercing of ears. This was done in accordance with the dogma, stating that a person cannot alternate his or her body which is created in the image of God.
Only thieves, pirates and representatives of the lower class continued to wear earrings."