A decade before Elon Musk founded his fast-rising rocket company, SpaceX, or spoke publicly about colonizing Mars, a different billionaire captivated the world with Biosphere 2.
Ed Bass, an oil tycoon, spent about $250 million to build and operate that facility as a proof-of-concept for a permanent, self-sustaining habitat on Mars. Four men and four women sealed themselves inside the airtight space in September 1991 and emerged two years later.
The experimental space-age facility served as the stage for a spectacular and controversial story of human endurance.
Built into a hillside of the Arizona desert during the early 1990s, the complex remains a functional marvel of engineering.
Business Insider recently visited Biosphere 2 to learn about the many challenges that early Martian colonists could face.
Here's what it's like inside the 3.14-acre bubble today.
Biosphere 2 is nestled in the foothills of the Santa Catalina Mountains in Oracle, Arizona. The area is part of the Sonoran Desert — an arid, unforgiving, and eerily Mars-like region that stretches from western Mexico into the US Southwest.
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A roughly 80-foot-tall glass pyramid poking out of the hillside greets visitors.
Source: Biogeosciences, Business Insider
Farther west in the sprawling 40-acre campus are other futuristic structures.
Source: "The Human Experiment," Business Insider
The architect Peter Pearce created Biosphere 2's space-age frame out of 77,000 steel struts and 6,600 silicon-lined glass panes to trap air inside. It can even withstand orange-size hail, which pummels Arizona about once every century.
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The first crew (there were two) walked through a modified submarine bulkhead on September 26, 1991, and sealed the airlock behind them. They wouldn't leave for two years. That entryway is where tours begin today.
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Business Insider's tour guide was John Adams, the facility's deputy director. Adams, who has worked there since the mid-1990s, is an expert on its complex systems, science, and history.
"It really showed us how little we truly understand Earth systems and how infinitely complex they are," Adams said of the first Biosphere 2 closure experiment. "There were a lot of people who said, 'You bottle this up, you close it up, it's just going to turn into a big ball of slime.'"
It didn't, and the eight crew members emerged alive — though they wound up needing some outside assistance.
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When the first crew of "biospherians" settled inside the complex, it trapped 7.2 million cubic feet of air — yet leaked only the equivalent of a thumb-size hole.
Source: "The Human Experiment," Biosphere 2, Business Insider
Though the facility was once a privately funded experiment in human survival, the University of Arizona bought it in 2011. It's now a scientific research facility, conference center, and tourist attraction.
Admission is $20 for an adult, with discounts for students, seniors, and military personnel.
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Biosphere 2 has seen about 3 million tourists and 500,000 students since 1991. The site also contains a village where visiting researchers can stay. It's quiet out there in the desert, save for the wailing of coyotes at dusk.
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Inside Biosphere 2, five "wilderness" zones — rainforest, ocean, savanna, marsh, and desert — emulated Earth's ecosystems. They helped scrub carbon dioxide from the air and generated oxygen. The crew lived in a connected habitat and farmed crops in an agriculture zone that's now called the hill slope.
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The kitchen was hallowed ground. Biospherians ate only what they could grow — mostly sweet potatoes and beans. It took four months to harvest enough ingredients to cook a pizza. Animals had to be raised and slaughtered to get meat. Coffee was a twice-monthly luxury.
Source: "The Human Experiment," Business Insider