On April 22nd We Celebrate Earth Day
The 1960s was a time period when people marched and rallied in the streets on a variety of issues from the civil rights movement to the movement against the Vietnam War. The decade also saw the beginning of wide-spread environmental awareness and concern.
The first Earth Day was held, across the U.S., on April 22nd 1970. It brought some twenty million Americans into the streets to say that humanity needed to pay more attention to how our society was impacting the rest of the biosphere. The years that followed would see a number of progressive pieces of environmental legislation adopted by the U.S. government, and other governments around the world, and would see an increase in participation in various types of ecologically oriented organizations and activities.
By 1990, however, it was clear that humanity still faced many environmental challenges and that some governments were, if anything, moving backward on environmental concerns.
So on the twentieth anniversary of the first Earth Day, a second mass mobilization was organized, Earth Day April 22nd 1990, this time taking the mobilization to a global level with several hundred million people participating in over a hundred countries.
Since that time Earth Day has been an annual event with various organizations participating around the world. The United Nations has declared April 22nd to be International Mother Earth Day and includes this day in its list of international days observed by the U.N.
For a more in depth, and very interesting, article on the history of Earth Day, read the Wikipedia article on Earth Day.