Gaylord Nelson, a U.S. Senator from Wisconsin, is credited with establishing Earth Day.
After witnessing the ravages of the 1969 Santa Barbara oil spill and inspired by the student anti-war movement, he called for an environmental teach-in, later called "Earth Day," to be held on Wednesday, April 22, 1970.
More than 20 million people participated that year, and now Earth Day is observed on April 22 each year.
Here are some classroom resources to help mark Earth Day:
The American Federation of Teachers' website features lesson plans that focus on the environment, including topics such as recycling, rain forests, earthquakes and preserving natural resources.
The TeacherVision website has K-12 lessons and other resources, including hands-on activities for science and art, to teach students about the environment and how to preserve our planet.
The Earth Network is creating a giant mosaic of images of people, animals and places directly affected or threatened by climate change — as well as images of people stepping up to do something about it — and their stories. You can post yours on the website.