Earth Day is observed around the world on April 22 to mark the day when people celebrate Earth, the only planet in the universe that can support life.
Earth Day started in 1970 and marked the beginning of the modern environmental movement, which united groups that had been fighting separately against polluting power plants and factories, oil spills, the indiscriminate dumping of raw sewage, pesticides, the extinction of wildlife and the loss of wilderness.
In 1969, a massive oil spill in Santa Barbara, Calif., drew the attention of the state's junior Democratic senator, Gaylord Nelson, who had long held concerns about the harm human activity was having on the environment in the United States.
Nelson enlisted the help of Republican Sen. Pete McCloskey, and the two recruited Denis Hayes, a young activist, to organize teach-ins at college campuses across the country. They chose April 22 for the teach-ins because it fell between spring break and final exams.
Following the example of organizers of the Vietnam War protests, Hayes built a staff of 85 to crisscross the country to promote Earth Day.
The idea took hold. The first Earth Day inspired 20 million Americans, or 10 percent of the country's population, and included faith groups, civic and business organizations and American citizens who took to the streets, auditoriums and parks to protest 150 years of industrialization that had left a legacy of health impacts.
Today, according to earthday.org
, more than a billion people around the world take part in Earth Day activities.