The United States had never experienced anything like it: On April 22, 1970, nearly one in 10 Americans flooded the streets and the woods and the seashores to call for an end to the merciless pollution of the country's air, waters, and landscapes. In the words of Senator Gaylord Nelson, the Wisconsin Democrat who conceived the idea of Earth Day, the goal was to force the issue of environmental protection "permanently onto the national political agenda"—and in that, the effort succeeded.

The conservation movement that existed before 1970 was largely made up of white, affluent outdoors-people who mostly focused on the protection of birds and other wildlife, the preservation of wilderness, and the establishment of parks and preserves. The environmental movement that was born on Earth Day aspired to something larger—a multiracial cause, propelled by the same passion that spurred the civil rights and anti–Vietnam War movements, dedicated to preserving urban environments as well as wild ones, and inspired by the ecological insight that our home is the whole planet.

Since then, the influence of Earth Day has waxed and waned; at times it has seemed little more than an occasion for corporate greenwashing. But the fieriness of the first Earth Day remains like an ember within the original idea. To mark Earth Day's 50th anniversary, Sierra assembled a collection of activists, organizers, and authors to imagine how it can be reinvigorated and reinvented. While each contributor writes in a different key, together they form a chorus, insistently hopeful that Earth Day 2020 can be another watershed moment—one that leads to a bigger, bolder, and more lasting transformation.