Before dawn on April 4, 1994 , Abigail Alling and Mark Van Thillo slipped across the foothills of Arizona’s Santa Catalina Mountains. They made their way to a looming monument of geodesic domes and pyramids known as Biosphere 2. The three-acre complex contained a miniature rain forest, a mangrove, a desert and a coral reef — along with seven people who had been sealed inside for a month.

Ms. Alling and Mr. Van Thillo had recently emerged from a two-year stay in Biosphere 2. Later, after they were arrested, they told reporters that they feared for the safety of the people inside. They were determined to bring the mission to an end.

They pulled open five of Biosphere 2’s doors and broke their seals. As outdoor air rushed in, they made their way to the ventilation system, where they smashed some glass panels.

That break-in effectively marked the end of one of the strangest experiments in the history of science. No one had ever built a sealed ecological world as big as Biosphere 2, and no one had ever survived so long inside one. The project would later be dismissed as a folly and a waste of effort. And yet, 25 years on, it’s an experiment worth rediscovering. Biosphere 2 might have some lessons to offer about managing Biosphere 1 — our planet.