On April 22, 1970, coordinated events took place in cities across the United States. An estimated 20 million people participated in a protest—still the largest single-day demonstration in American history. What sparked such a massive turnout? In many ways, a single image.

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But the impact of that image cannot be understood without considering the broader cultural context in which it emerged.

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The turbulence of 1960s America had given rise to a generation hungry for change. It was the decade of the Civil Rights Movement, rock and roll, and the Vietnam War. At the same time, the environmental consequences of the industrial revolution were becoming impossible to ignore.

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In 1962, Silent Spring, a book by Rachel Carson, exposed the devastating effects of the widespread and indiscriminate use of the pesticide DDT. In 1969, an oil well off the coast of Santa Barbara, California, spilled more than 3 million gallons of oil, polluting 800 square miles of ocean and killing over 10,000 seabirds, dolphins, seals, and other marine life. Smog choked cities. Toxic pollution flowed into waterways. In Ohio, the Cuyahoga River caught fire—which happened at least 14 times.

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But in 1968, while orbiting the Moon, astronaut William Anders took a photograph:

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Titled Earthrise, the image showed Earth as a small blue sphere suspended in the black emptiness of space. In stark contrast to traditional landscape photography—where land seems to stretch on infinitely—this photo conveyed a sobering truth: our planet is finite and fragile. The lunar surface in the foreground—barren, lifeless, and inhospitable—underscored the fact that Earth is our only home.

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Nature photographer Galen Rowell called Earthrise “the most influential environmental photograph ever taken.”1 It became a symbol of Earth Day and a rallying point for the growing environmental movement. This movement helped bring about significant policy changes, including the creation of the Environmental Protection Agency, the National Environmental Education Act, the Occupational Safety and Health Act, the Clean Air Act, and the Endangered Species Act.

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More than 50 years later, as we grapple with climate change, population growth, habitat loss, and more, Earthrise and images like it remain powerful reminders: we have only one planet—and we must protect it, both from ourselves and for ourselves.