Below is some history on how Earth Day came about, my friend actually thought it was a made up holiday by Hallmark!
Earth Day is a day designed to inspire awareness and appreciation for the Earth's environment. It was founded by U.S. Senator Gaylord Nelson as an environmental teach-in held on April 22, 1970. Earth Day is celebrated in spring in the Northern Hemisphere and autumn in the Southern Hemisphere. Earth Day Network, a group that wishes to become the coordinator of Earth Day globally, asserts that Earth Day is now observed on April 22 on virtually every country on Earth. World Environment Day, celebrated on June 5 in a different nation every year, is the principal United Nations environmental observance. Many communities also celebrate Earth Week, an entire week of environment-related activities, the first of which occurred in Philadelphia in 1970 (starting April 16 and culminating on Earth Day, April 22.)