Earth Day began in the United States in 1970 as an environmental teach-in created by then-Wisconsin Senator Gaylord Nelson. A precursor to the modern environmentalism movement, Earth Day now is observed annually by more than 500 million people and governments in 175 countries. The first Earth Day was a huge driver of environmental policy. Soon afterward, Congress passed the Clean Air Act, the Clean Water Act, the Endangered Species Act, and Superfund.

This year will mark the 38th annual observance of Earth Day with rallies, celebrations, hikes, fairs, festivals, and seminars, and many more events across the globe.