Penny Chisholm is a biological oceanographer who holds a joint appointment between MIT's departments of Civil and Environmental Engineering and Biology. Her research focuses on understanding of the role of microorganisms in shaping marine ecosystems. It is centered on understanding the biology and ecology of Prochlorococcus, the smallest and most abundant photosynthetic microorganism on Earth. Discovered only 30 years ago, it numerically dominates large regions of the world’s oceans and is responsible for a sizable fraction of ocean photosynthesis. In addition to her scientific publications, Chisholm has published (with Molly Bang) three award-winning children’s picture books — Living Sunlight, Ocean Sunlight, and Buried Sunlight — which describe the central role of photosynthesis in shaping life on Earth. Chisholm has been a member of the MIT Faculty since 1976. She is a member of the National Academy of Sciences and the American Academy of Arts and Sciences, has been a Guggenheim Fellow, and has received the Alexander Agassiz Medal, the Margalef Prize in Ecology, and the National Medal of Science. Twitter: @ChisholmLab_MIT