From The Old Farmer's Almanac,
Ever wondered how Earth Day started? This observance arose from an interest in gathering national support for environmental issues.
In 1970, San Francisco activist John McConnell and Wisconsin Senator Gaylord Nelson separately asked Americans to join in a grassroots demonstration.
McConnell chose the spring equinox (March 21, 1970) and Nelson chose April 22.
Millions of people participated, and today Earth Day continues to be widely celebrated with events on both dates.
The most common practice of celebration is to plant new trees for Earth Day.