Rachel Carson's seminal work Silent Spring was published in 1962, selling more than half a million copies worldwide. In the book Carson lays out a tragic future where animal, plant, and even human life is radically effected by pollution, toxic waste, and other by-products of human industry and fossil fuel usage. Public awareness of and outcry against the environmental impact of human activity increased exponentially; many credit Silent Spring as the birth of the environmental movement.

On January 28, 1969, Union Oil's Platform A off of the coast of California experienced a blow-out that led to the then largest oil spill in U.S. history (and still third behind the Deepwater Horizon and Exxon Valdez spills). Roughly 100,000 barrels of crude oil spilled into the waters of the Santa Barbara Channel. The primary cleanup took 45 days; oil seeped from the well through 1970 (though at a greatly reduced rate). At least 3,500 sea birds died plus an unknowable number of other sea creatures, including animals from the sea lion and elephant seal colonies on San Miguel Island.

Reportedly driven to act after seeing the 800 mile long spill from the air, Senator Gaylord Nelson (D-WI) began the process that would lead to the first Earth Day. With assistance from Congressman Pete McClosky (R-CA), Senator Nelson recruited a young and motivated team to organize a national day of education and action; that team was headed by Dennis Hayes, then a 25 year old Harvard student.

Tapping the energy and spirit of the anti-war movement, the Earth Day organizers actively reached out to colleges, schools, and other youth organizations (as well as a famous ad in the New York Times). Ultimately an estimated 20 million people participated throughout the U.S., through teach-ins, local cleanups, lectures, and a host of other events. The city of New York shut down Fifth Avenue to host Earth Day demonstrations, and Union Square saw crowds of up to 20,000 people at a time. Roughly 2,000 colleges and universities held events, as well as approximately 10,000 primary and secondary schools. The date, April 22, wasn't chosen with any symbolic reason; it simply happened to be a Wednesday between spring break and finals - when the most students would be present on college campuses.

In terms of its reach and impact, the first Earth Day was an unmitigated success.