Thursday will be the 51st Earth Day, an event celebrated by more than one billion people in 193 countries worldwide, currently coordinated by the Earth Day Network.
Earth Day's origins start with Wisconsin Sen. Gaylord Nelson, who was inspired to organize the event after the Jan. 28, 1969 Santa Barbara oil spill. More than three million gallons of oil spilled into the Santa Barbara Channel in the Pacific Ocean, killing more than 10,000 animals. Nelson enlisted Stanford University graduate Denis Hayes to assist in coordinating and organizing the event.
The first Earth Day was held April 22, 1970. The New York Times estimated the gather in in New York City had crowds of 20,000 people and more than 100,000 over the course of the day. Since New York City was home of most television networks and several large publications, coverage of Earth Day was spread nationally.
Across the country, approximately 2,000 colleges and universities and approximately 10,000 schools participated in the first Earth Day, according to the Environmental Protection Agency. The first Earth Day was said to bring 20 million Americans together, pressuring the United States to prioritize environmental issues.
"My primary objective in planning Earth Day was to show the political leadership of the nation that there was broad and deep support for the environmental movement," Nelson said in 1980. "While I was confident that a nationwide peaceful demonstration of concern would be impressive, I was not quite prepared for the overwhelming response that occurred on that day."
The first Earth Day's success didn't take President Richard Nixon by surprise, having representatives around the country at events. On July 9, 1970, Nixon proposed consolidating the environmental responsibilities of the U.S. government into one agency, the EPA.
In the 50 years since its inception, Earth Day continues to influence the environment on both local and international scales.
In 1995, Nelson was awarded the Presidential Medal of Freedom in recognition of his environmental work. He passed away in 2005 at the age of 89.