Jean-Jacques d'Ortous de Mairan (November 26, 1678 - February 20,1771) was a French geophysicist, astronomer and chronobiologist. In 1698 he went to Paris to study mathematics and physics. In 1702, he returned home and began his lifelong study of several fields, most notably astronomy and plant rhythms. In 1729, he performed an experiment that demonstrated the existence of circadian rhythms in plants, specifically the Mimosa pudica. He was intrigued by the daily opening and closing of the heliotrope plant and performed a simple experiment where he exposed the plants to constant darkness and recorded the behavior. His key conclusion was that the daily rhythmic opening and closing of the leaves persisted even in the absence of sunlight. His observations and experiments also inspired the beginning of what is now known as the study of biological circadian rhythms. Over the course of his life, he was elected into numerous scientific societies and made key discoveries in a variety of fields including ancient texts and astronomy. He died of pneumonia in 1771 at the age of 92.