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Prior to the first Earth Day celebration in 1970, most landmark environmental regulations and laws were yet to be passed. It was completely legal for a factory to emit massive black clouds of toxic smoke into the air or dump tons of toxic waste into nearby waterways. Air pollution was commonly accepted as the sight and smell of a prospering nation, leaving mainstream America oblivious to environmental concerns.

In 1962, the publication of Rachel Carson’s Silent Spring marked a powerful impact on the growth of environmental consciousness. With more than 500,000 copies sold in 24 countries, the bestseller became a rallying point for the new social movement in the 1960s, focusing on the indissoluble links between pollution and public health. Earth Day 1970 provided a voice to the emerging movement.

Wisconsin Senator Gaylord Nelson came up with the idea for a national day to focus on the environment as a result of a massive oil spill in Santa Barbara, California, in 1969. Noticing the power behind the student anti-war movement of the time, Senator Nelson sought to harness the energy behind the anti-war protests and merge it with the growing public concern for air and water pollution in order to force environmental protection onto the national political agenda.

April 22 was selected as the date and in 1970, massive coast-to-coast rallies comprising of 10 percent of the total United States population at the time took to streets, parks, and campuses in order to demonstrate for a healthy and sustainable environment. Earth Day united groups across political and socioeconomic boundaries that had been fighting individually against oil spills, polluting factories and power plants, raw sewage, toxic dumps, pesticides, freeways, the loss of wilderness, and the extinction of wildlife. The first Earth Day led to the formation of the United States Environmental Protection Agency as well as the passage of the Clean Air, Clean Water, and Endangered Species Acts.

Twenty years after the first Earth Day celebration, in 1990, Earth Day became a global celebration, mobilizing 200 million people in 141 countries. Today, Earth Day is widely recognized as the largest secular observance in the world, marked by more than a billion people every year as a day of action to change human behavior and provoke policy changes.

On its 50th Anniversary, Earth Day will return to its roots from 1970, placing environmental progress among the best ways to improve our world.