Earth Day is on April 22nd each year.

Earth Day started in 1970. 1970 in the United States brought with it (among other events) the Kent State shootings, the advent of fiber optics, "Bridge Over Troubled Water," Apollo 13, the Beatles' last album, the death of Jimi Hendrix, the birth of Mariah Carey, and the meltdown of fuel rods in the Savannah River nuclear plant near Aiken, South Carolina -- an incident not acknowledged for 18 years.

Earth Day founder Gaylord Nelson, then a U.S. Senator from Wisconsin, proposed the first nationwide environmental protest "to shake up the political establishment and force this issue onto the national agenda. " "It was a gamble," he recalls, "but it worked."

Earth Day 1970 achieved a rare political alignment, enlisting support from Republicans and Democrats, rich and poor, city slickers and farmers, tycoons and labor leaders. The first Earth Day led to the creation of the United States Environmental Protection Agency and the passage of the Clean Air, Clean Water, and Endangered Species acts.

In 1990, a group of environmental leaders asked Denis Hayes to organize another big campaign. This time, Earth Day went global, mobilizing 200 million people in 141 countries and lifting the status of environmental issues on to the world stage. Earth Day 1990 gave a huge boost to recycling efforts worldwide and helped pave the way for the 1992 United Nations Earth Summit in Rio de Janeiro.

Earth Day 2000 combined the big-picture feistiness of the first Earth Day with the international grassroots activism of Earth Day 1990. For 2000, Earth Day had the Internet to help link activists around the world. By the time April 22 rolled around, 5,000 environmental groups around the world were on board, reaching out to hundreds of millions of people in a record 184 countries. Events varied: A talking drum chain traveled from village to village in Gabon, Africa, for example, while hundreds of thousands of people gathered on the National Mall in Washington, D.C., USA.