The Most Abundant Species on Earth

Sallie (Penny) Chisholm, Faculty

The cyanobacterium Prochlorococcus may be the most abundant single species on Earth, but it remained unknown until 1988. Chisholm’s discovery of the photosynthetic organism that is responsible for every fifth breath we take revolutionized our understanding of how microbial life shapes the chemical composition of the world’s oceans and atmosphere. Chisholm is a recipient of the National Medal of Science.