In this episode I speak to Sallie "Penny" Chisholm, the Lee and Geraldine Martin Professor of Environmental Studies at MIT. Dr. Chisholm studies photosynthesis—the way life harnesses the energy of the sun. Plants carry out photosynthesis, but so do microbes in the ocean. Dr. Chisholm studies the most abundant of these photosynthetic microbes, a species of bacteria called Prochlorococcus. There are a trillion trillion Prochlrococcus on Earth. Dr. Chisholm researches these microbial lungs of the biosphere, and how they produce oxygen on which we depend.

Along with her scientific research, Dr. Chisholm is also the author of a new children's book, Living Sunlight: How Plants Bring The Earth To Life.