Inspired by anti-war "teach-ins" and the activist culture of the late 1960s, United States Senator Gaylord Nelson of Wisconsin organized the first Earth Day on April 22, 1970, to raise awareness of environmental issues and elevate the state of the environment into mainstream political discourse. Rachel Carson's book, Silent Spring (1962), examined why there were increasing levels of smog in the nation's cities, and focused attention on environmental disasters such as the Santa Barbara oil spill (1969) and the fire on Cleveland's Cuyahoga River due to oil and chemical pollution (1969), and gave rise to local groups of concerned citizens and activists. Enlightening photographs of the Earth taken by astronauts underscored the fact that we inhabit a finite system, small in comparison with the vastness of the solar system, and changed the way people visualized the planet. On that first Earth Day, an estimated 20 million people participated in peaceful demonstrations, lectures...