Thursday marks the 40th anniversary of Earth Day, and millions across the world will gather to participate in festivals and bike rides, clean area parks, plant trees and attend sustainability fairs. Instead of one large celebration, there will be countless of celebrations across the world—which is exactly how founder and Sen. Gaylord Nelson of Wisconsin, wanted Earth Day and ultimately Earth Week to be celebrated.

Nelson viewed the effects of an oil spill in Santa Barbara and read an article about teach-ins held on college campuses when he decided such a demonstration could bring environmental issues into the spotlight and ultimately show Washington that Americans were ready to act. In a speech given in Seattle on Sept. 20, 1969, he announced his intentions and the idea spread rapidly. His office was inundated with requests for information, but Nelson was determined to keep at a local level. While his office helped plan and provide ideas, they were not in charge of all of the events.

Even now, 40 years later, Earth Week events are coordinated locally and not nationally. The time of year was chosen intentionally to avoid holidays, midterms and final for students and as much as possible ensure the likelihood of good weather for participants. The first Earth Day was considered a huge success and even beyond Nelson’s expectations.