Final answer:
Earth Day was the brainchild of Wisconsin senator Gaylord Nelson, who suggested setting aside April 22, 1970, as a day of learning and discussion of environmental issues.
Step-by-step explanation:
Earth Day was the brainchild of Wisconsin senator Gaylord Nelson. In response to increasing concerns about environmental issues, Nelson suggested the idea of setting aside April 22, 1970, as a day of learning and discussion of environmental issues. This idea was embraced by colleges and universities, and Earth Day has been observed every year on April 22 since then.