Taber MacCallum and Jane Poynter witnessed the most affecting solar eclipse of their lives in 1992. That's because as they watched the Sun disappear behind the Moon’s shadow, they were also watching their oxygen supplies slipping away.

At the time, they and their six teammates were sealed inside Biosphere 2, a 91-foot-tall, 3.14-acre experimental complex outside Tucson, Arizona. “We were all just glued to the monitors,” MacCallum recalls, “because you can see when the Sun was hidden away by the Moon, for that half hour period, the CO2 started going up. The oxygen started going down. You could see the actual, palpable effect.”

Without the Sun, the plants around them had stopped photosynthesizing and producing oxygen. Earth’s atmosphere is so huge that half an hour of this during a solar eclipse doesn’t have a noticeable effect. But inside an atmosphere 19 trillion times smaller than Earth’s, MacCallum and Poynter noticed.

“It's very hard on the Earth to get that tight a visceral connection between your behavior and the environment,” MacCallum says.

Today, the imposing white dome of Biosphere 2 still rises above the Arizona desert like a cross between a greenhouse and the Taj Mahal. Now, it’s a research station maintained by the University of Arizona where researchers study Earth processes, global environmental change, weathering, landscape evolution, and the effect of drought on rainforests, among many projects. Because of its systems and size, scientists can do controlled experimentation at an unprecedented scale in Biosphere 2.

Another view of Biosphere 2. Image credit: © CDO courtesy of the University of Arizona

 
MacCallum and Poynter returned to Biosphere 2 in May 2016 for the One Young World Environmental Summit to speak to young environmental leaders from around the world. But in the early 1990s, they and six others were sealed inside it for two years and 20 minutes, from September 26, 1991 to September 26, 1993, in a life-changing experiment that was equal parts humility and hubris—both shortsighted and ahead of its time.

“The big questions of the two-year mission,” says MacCallum, were, “Can we build artificial biospheres? Can these be objects of science? Can we learn from them?”

We could and did. As a result of their voluntary containment, we learned how to seal a giant building so that it loses less air than the International Space Station, manage damaged coral reefs, feed eight people on a half-acre of land, and recycle water and human waste in a closed system, among other things.

The structure itself, built from 1987 to 1991, is a technological marvel even today. The idea was to build a miniaturized biosphere completely separated from Earth, see if humans could live inside it, and see how they affected the animals and plants around them and vice versa. (Why call it Biosphere 2? Because Earth is Biosphere 1.) It’s roughly as tightly sealed as the space station and separated from the soil around it by a 500-ton steel liner.

In the early '90s, when the mission started, the ideas that humans were causing climate change or even that Earth was a biosphere at all were much less accepted than they are today. “When we started this project, I was spelling the word ‘biosphere’ down the phone,” says MacCallum.

Much the way a botanical garden's conservatory is, Biosphere 2’s glass-walled domes and pyramids were filled with different biomes: rainforest, ocean (with a coral reef), savannah, desert, mangrove swamp, and agricultural fields in which the team grew all their crops. They ate so many sweet potatoes that Poynter turned orange, but their world also included domestic animals: goats (their only dairy source), chickens, pigs, and tilapia. They had only enough coffee plants to make one cup of coffee per person every few weeks.

The desert biome in Biosphere 2. Image credit: © CDO courtesy of the University of Arizona

 
Problems quickly developed. The coral reef became overgrown with algae. Most of the pollinating insects died. A bush baby in the rainforest biome got into the wiring and was electrocuted. Each of the crew members had a primary job: Poynter was in charge of the farm and farm equipment, and MacCallum was in charge of the analytical chemistry lab inside Biosphere 2. The crew had to do all their research, farming, and experiments while hungry because they weren’t getting enough calories.

More dangerous was the decline in oxygen. That night in 1992, their oxygen levels dipped temporarily, but overall their oxygen levels declined from 20.9 percent to 14.5 percent. (Any environment below 19.5 percent oxygen is defined as oxygen-deficient by the Occupational Safety and Health Administration, or OSHA.) The low oxygen made them lethargic. For months they couldn’t sleep properly because it gave them sleep apnea. Scientists were monitoring them and communicating with them from the outside, and finally in August 1993, just a month before the crew left Biosphere 2, they decided to start pumping in oxygen.

Taber MacCallum tests air conditions in Biosphere 2. Image credit: © CDO courtesy of the University of Arizona

 
Later, scientists figured out that the culprits were microbes proliferating in the Biosphere’s compost-rich soil, combined with the building’s concrete. The microbes themselves were not harmful, but they converted oxygen into carbon dioxide, which then reacted with the building’s concrete to form calcium carbonate and irreversibly remove oxygen molecules from the Biosphere's atmosphere.

Still, looking back more than two decades years later, MacCallum and Poynter view the experiment as a success. Its initial science findings have been developed on in the years since—the University of Arizona has owned the facility since 2007—and its research focus remains as big picture as it ever was: global environmental change.

Beyond the science, even just seeing Biosphere 2 could change people’s perspectives. Poynter recalls getting an email while she was inside Biosphere 2 from a man who walked around the perimeter of the structure as part of the monitoring effort, who said, “'I get it now, because I walked around Biosphere 2, this miniature version of planet Earth, and it smacked me in the face: you guys only have what you have in there, and you have nothing else.'”

“That is fundamentally the message: that it's finite,” Poynter says. “And also very resilient.”

When after two years they finally emerged, Poynter had lost virtually all the enzymes to digest meat from eating so little of it. Nevertheless, she says, “Physically, we were in pretty decent shape. I had spent every day farming, so I was pretty strong.”

Jane Poynter checks on the goats in Biosphere 2. Image credit: © CDO courtesy of the University of Arizona

 
Still, it was a huge change. “The experience of coming out of Biosphere 2 was amazing in that it was like being reborn into this world and seeing it with fresh eyes,” she recalls. That night they had a big party with friends they hadn’t seen in two years. “And then the next morning there was this giant pile of garbage. It was this stark reminder of this consumable world that we live in.”

Poynter and MacCallum, who were dating when they entered Biosphere 2, married nine months after leaving it. Together with three others, they formed Paragon Space Development Corporation. Over the years, they developed a range of aerospace technology, including temperature control and life support systems for NASA and SpaceX that could be used to support people on the Moon or on Mars.

Their current company, World View Enterprises, spun out of Paragon in 2013. Key staff include chief scientist Alan Stern, head of the New Horizons mission to Pluto, and astronaut Mark Kelly (twin brother of astronaut Scott Kelly), who is the director of flight crew operations. World View sends uncrewed vehicles high up in the near-space stratosphere to research weather and other phenomena, and aims to one day bring people up to where the sky is black, the Earth looks curved, and it’s visibly clear that Earth is the home we share.

The curvature of the Earth as captured by a World View craft. Image credit: World View

 
It's that big-picture view that Poynter and MacCallum want to share with others. After talking with astronauts, they think that the “overview effect” astronauts feel when seeing the Earth from space is not unlike what they felt in Biosphere 2. Like Poynter and MacCallum, astronauts describe feeling deeply moved by the experience to do something to help Earth and its people.

Poynter says the company’s technology is proprietary and has to do with buoyancy control. “The basis of it is our ability to do very accurate altitude control,” she says, which allows their vehicles to take advantage of prevailing winds at different altitudes to travel exactly where they want.

World View Enterprises is particularly interested in taking leaders and influencers up to the stratosphere. Because you can’t just lock world leaders inside a biosphere in the desert for two years to give them the insight that Poynter and MacCallum know so deeply: We, as humans, are fully connected to and dependent on our environment.

“In the biosphere," Poynter says, "I really fell in love with the Earth."