The April 22 Earth Day, founded by Senator Gaylord Nelson, was first organized in 1970 to promote ecology and respect for life on the planet as well as to encourage awareness of the growing problems of air, water and soil pollution.
Some people prefer to observe Earth Day around the time of the March equinox. In 1978, American anthropologist Margaret Mead added her support for the equinox Earth Day, founded by John McConnell. She stated that the selection of the March Equinox for Earth Day made planetary observance of a shared event possible.
Source: Text: Timeanddate.com
2016 Theme: Trees for the Earth
Earth Day was first celebrated in the United States in 1970 and is organised by the Earth Day Network. Its mission is to broaden and diversify the environmental movement worldwide and to mobilize it as the most effective vehicle to build a healthy, sustainable environment, address climate change, and protect the Earth for future generations. With this year’s theme, looking forward to its 50th anniversary, it sets the goal of planting 7.8 billion trees over the next five years.