The first Earth Day took place on April 22, 1970. It was marked by more than twelve thousand events across the country with more than 35,000 speakers, including some two-thirds of the members of Congress. Millions participated. A remarkable success, it led to the Clean Air Act of 1970, the Clean Water Act of 1972, the Endangered Species Act of 1973, and to the creation of the Environmental Protection Agency. Adam Rome is Assistant Professor of Environmental History at the University of Delaware and author of The Genius of Earth Day: How a 1970 Teach-In Unexpectedly Made the First Green Generation.