Earth Day is celebrated on April 22 each year in the United States and on either April 22 or the day the spring equinox occurs throughout the rest of the world. It began in 1970 as a movement to educate the public about environmental issues. The first Earth Day intended to raise awareness of pollution and to bring environmental issues into the national spotlight.
"Earth Day is not a federal holiday, though public laws designated Earth Day on March 21, 1975 (P.L. 94-8); April 22, 1990 (P.L. 101-186); and April 22, 1991 (P.L. 102-34). Resolutions introduced in the 92nd Congress (1971-1972) and 93rd Congress (1973-1974) would have designated either April 22, the third Wednesday of April, or March 21 (the vernal equinox) as Earth Day on an annual basis, but no further action was taken.7 Legislation introduced in the 106th Congress (1999-2000) would have designated April 22 as Earth Day, but no further action was taken.8 The United Nations designated April 22 as International Mother Earth Day in 2009. The United Nations also has designated June 5 as World Environment Day since 1974." Source: CRS
The first Earth Day, held on April 22, 1970, was the brain-child of Wisconsin Senator Gaylord Nelson and activist Denis Hayes. They were inspired to take action by a massive oil spill in Santa Barbara, California, in 1969. With strong backing from Walter Reuther of the United Auto Workers, celebrations and teach-ins took place in 2,000 U.S. colleges and universities, and roughly 10,000 primary and secondary schools. In addition, hundreds of communities throughout the country participated, bringing the total number of participants to 20 million, or about 10% of the U.S. population at the time. With this event as a catalyst, by the end of 1970 the U.S. Environmental Protection Agency (EPA) was created, and new environmental laws were passed, including the National Environmental Education Act, the Occupational Safety and Health Act (which formed OSHA), and the Clean Air Act, followed two years later by the Clean Water Act, and after that the Endangered Species Act and the Federal Insecticide, Fungicide, and Rodenticide Act. In 1990, Hayes organized a global Earth Day, with more than 200 million participants in more than 140 countries. Earth Day now brings together citizens and activists from around the world to raise awareness and take action regarding such environmental concerns as global warming and renewable energy.
To learn more about Earth Day check out the website tab for links on Earth Day.
Last 24 years themes of Earth Day are given below:
Source: Earth Reminder for Everyone