Earth Day as we know it began 45 years ago today.

Despite being a completely new holiday, Wednesday, April 22, 1970 saw crowds of millions turn out for peaceful demonstrations in support of environmental reform in the United States.

The primary reason for choosing the April 22 date was that it would be a convenient day for the schedules of college students. It fell between spring break and finals, and didn’t overlap with major religious holidays. US Senator Gaylord Nelson, who is credited as having chosen the date, envisioned the day would be one of national activism on college campuses, in which people would educate themselves and each other about environmental issues.

In some ways the first Earth Day in 1970 was the culmination of a rising movement that began expressing environmental concerns in the 60s. In other ways, it marked the beginning of a new era of environmentalism. Later in 1970 the United States passed an extension to the Clean Air Act of 1963 which, among other things, founded the Environmental Protection Agency, and granted that agency the power to enforce environmental regulations. In the years that followed, laws to protect water and endangered species were passed in the US.

Today, we celebrate Earth Day on April 22 worldwide, and it is one of the largest secular holidays in terms of the amount of people who celebrate it. Even though it is ceremonial in many ways, we’d do well to keep in mind Earth Day’s origin as a day of action, and to try and build on that legacy. Now more than ever, our planet could use concrete steps toward preservation, whether it’s planting a tree in your neighborhood or supporting environmental legislation, let this Earth Day collection inspire you to make a difference on this ambitious, storied holiday.