Biosphere 2

Just outside the town of Oracle, Arizona, nestled between the seemingly endless plains of the Sonaran desert and the cactus-pocked foothills of Mount Lemmon, stands an enormous glass ziggurat: Biosphere 2.

Built in the late ‘80s at the behest of an oil tycoon, the structure was intended to be a small-scale model of a self-contained ecosystem—hence the name—the earth itself is “Biosphere 1″. Constructed with an airtight seal, Biosphere 2 was built to see if humans could sustain themselves in a completely “closed system”—recycled water, oxygen and food supplied by plants grown under the glass, nothing but electricity and the sun’s energy entering or leaving. Part living art installation, part science experiment, the “human enclosure”—as B2’s staff calls it—involved eight people and lasted two years out of the three planned, due to a number of closely-scrutinized technical difficulties—by its end, it was one of the most well-known and controversial science experiments ever conducted. It was also the subject of an abysmal spoof film starring Pauly Shore (boasting an astounding 5% on RottenTomatoes) and, what’s more, it was the site of the 2016 APS Committee on Informing the Public meeting, meaning the PhysicsCentral crew got to check out this extraordinary feat of ambition and engineering!

For starters, it’s worth giving a little more background on why we were there. The Committee on Informing the Public (CIP for short) is a rotating group of about a dozen experts from the fields of physics and science outreach, who meet every year to discuss new ways to spark interest in the physical sciences. 

After the deliberations and meetings, we got to take a trip “under the glass” for an exclusive tour of B2, where we learned about the history of the project and the modern research that’s being performed in this amazing, one-of-a-kind structure.

Our first stop under the glass was the landscape evolution observatory (or LEO for short), constructed in the space formerly occupied by the half-acre farm that supplied the “biospherians” with food. Since the decommissioning of the facility, most of it has lost its hermetic seal, but the LEO has remained relatively airtight, allowing it to be used for research.

Our tour guide joked that it looks like they’re “farming dirt”—in reality, the three arched
enclosures of the LEO are used to study the effect of varying atmospheric CO2 on soil erosion.

After the LEO, we were led on to explore the “biomes”—model ecosystems, each styled after a different environment found on Earth. Our first stop was the rainforest, a dense jungle complete with a babbling waterfall and the dizzyingly thick smell of oxygen.

As much fun as it would have been to explore the rainforest, we weren’t allowed beyond a small observation deck. From there, however, we could see why this part of the biosphere was practically opaque from the outside—the more ambitious trees had formed a canopy, their leaves crowded all the way up against the glass. When the human enclosure was begun, we were told, you could see every plant in the biome from the observation deck, but after this many years the trees have grown tall and dense, and the thick curtain of young vines streaming down from the treetops obscured our vision, hiding anything more than twenty feet away. At the project’s outset, the biome also contained a small nocturnal primate called a bush baby. The fate of the creature is something of a mystery; all we were told is that it didn’t survive the experiment, but one member of our party swears she heard a former biospherian joke that “we got really hungry in there”.

While the bit about the bush baby was hopefully a joke, the hunger definitely wasn’t. Although the soil included in their half-acre farm was fertile and there was ample water (recycled from the human inhabitants’ waste), influences from half a world away would spell trouble for the farmland’s yields. The human enclosure commenced in September of 1991, but three months prior, Mt. Pinatubo—a volcano in the Philippine islands—spewed out one of the largest volcanic eruptions in recent memory. The cloud of ash and dust created by Mt. Pinatubo’s eruption altered weather patterns as far away as Arizona’s Sonaran desert, leading to an unusual number of overcast and cloudy days. While the effects of this eruption impacted communities around the world, they were perhaps felt most acutely within Biosphere 2, where the intensity of the sun’s rays was the absolute limiting factor on the availability of food. The scarcity split the biospherians into factions. Half of them wanted supplementary food supplies, while the other half insisted that unforeseen conditions were a part of the experiment, and that receiving external help would compromise the integrity of their “mission”. Tensions ran high as crew members began to lose weight under serious food rationing, performing up to 14 hours of physical labor each day on fewer than 2000 calories. In the end, the biospherians held out without externally-supplied nutrition, but the food crisis undoubtedly contributed to the experiment’s early termination. More on that later, though.
From the rainforest, we were guided out onto a walkway overlooking B2’s artificial ocean, a 676,000-gallon wave pool home to multiple species of tropical fish and a diverse coral ecosystem. Like the rest of B2, the ocean aims to be “self-contained”—that is, no food or nutrients are added to it, and the fish that live in it subsist entirely on the algae and plankton that grow naturally thanks to photosynthesis. Several thousand gallons of “starter” water were actually trucked in from the Pacific Ocean to fill the pool, to ensure that all the diverse microbial components of a healthy ocean ecosystem would be present in B2’s ocean. Once that was in place, salt water was mixed to the appropriate concentration and the mixture was topped off. The waves and tides of the ocean are simulated by an enormous vacuum apparatus that, every few minutes, rapidly sucks in a huge volume of water and lets it flood out again. The noise this makes is a little horrifying—like something vast and mechanical breathing—but the churning of the waves is absolutely essential to properly simulate an ocean environment. Slowly, the stones on the “beach” will be eroded into sand.

If you look closely, you can see the heads of several divers receiving their SCUBA
certification—B2’s simulated ocean is the largest body of water around for miles. 

We made our way along the walkway, we passed over a mangrove forest with its roots dipped into the ocean and into the savanna biome, where strange, tentacled cacti and other exotic (at least to my Northeastern mind) plants grew. To our right, an aquaponics setup—a project from a nearby school, apparently—burbled quietly as water from a small fishtank trickled through several terraced planters, home to a fledgling crop of strawberries. A few fruit trees formed a small orchard, intended to supplement the Biospherians’ food supply, but the majority of the savanna serves as a transition zone between the rainforest and the desert that lay at the other end of the biosphere.

Further along the walkway, the plants started to thin out, and trees gave way to the scrubby grasses and cacti growing among the sandy terrain and artificial boulders of B2’s desert environment. A bird flitted in through a window, no longer sealed shut this long after the original experiment was abandoned. 

There’s a funny story about those artificial boulders, though—what was intended as a minor aesthetic touch ended up being one of the biggest problems with the experiment, necessitating the first deliberate “breach” of the project’s containment. Most of the rocks inside Biosphere 2 were brought in from the surrounding desert, but for all the ones above a certain size, it was decided that it would be easier to “construct” the rock formations on-site using concrete.
Several months into the human enclosure, it was noticed that oxygen levels under the glass had been dropping precipitously. Plant activity hadn’t changed, as evidenced by the fact that CO2 levels stayed relatively constant, but the fact remained that the Biospherians’ oxygen supply was being depleted to potentially dangerous levels. While the calorie restriction necessitated by the decreased sunlight was inconvenient, it was survivable. The oxygen situation was another story, and so oxygen was injected into the facility to keep the Biospherians alive and the experiment running.
It wasn’t until after the experiment was terminated that the source of this mysterious oxygen deficit was discovered, when scientists introduced particles of a radioactive oxygen isotope into the environment. This allowed them to go in with a Geiger counter (a radiation detector) and track down the radioactive tracer particles, to see where they had gone. To everyone’s surprise, the concrete “rocks” set off the Geiger counter! While it’s ordinarily hard enough to walk on after a few days, concrete actually takes about 100 years to harden (or “cure”) completely. This process requires oxygen, to turn calcium compounds in the wet concrete into calcium carbonate—and so the exposed concrete of the rocks was sucking the oxygen out of the air.
The desert was the last of the “biomes” we got to visit, but the tour wasn’t quite over; below the glass enclosure, several hundred feet of maintenance tunnels houses the vast array of complex machinery that keeps the facility running—all designed to be run and maintained by a single Biospherians with engineering experience. Probably the most impressive demonstration of physics from B2 came at the very end of the tour, though, in the form of  the Biosphere’s “lung”.
When you’ve got a temperature change in an enclosed, airtight space—even of just a few degrees—things can get hairy. Hotter air is less dense, meaning it takes up more space, but if the volume of a chamber is constant (like in a sealed glass jar), then the rising temperature manifests as an increase in the air pressure. While humans can handle slight changes in air pressure, these can be disorienting, and it puts strain on the sealed points as air tries to escape. The engineers who designed Biosphere 2 foresaw this problem in the hot Arizona sun, and got around it in a fantastically clever way.
B2’s “lung” is an enormous circular chamber with a roof made of galvanized rubber, all enclosed in an opaque dome to protect against the degrading effects of the harsh sun. As the sun heated the air inside B2 over the course of the day, it would expand, forcing up the flexible roof of the lung chamber—along with the ten-ton steel weight at the center of the membrane. When nighttime came, the weight would pull the chamber’s roof back down again, coming to rest on the steel legs you see in the photo above.
Now that the facility is no longer airtight, the lung isn’t necessary, but they keep two 5 horsepower fans running within it as a demonstration—those two fans are all it takes to suspend the enormous weight a few dozen feet off the ground. As we exited, taking a small arched doorway from the lung into the dry desert air, we were shepherded out by a strong gust of wind, thanks to the pressure differential between inside and out. 
All in all, visiting Biosphere 2 was an incredible experience and one that I’d highly recommend if you ever find yourself passing through that lonely part of Arizona.
What happens when several thousand distinguished physicists, researchers, and students descend on the nation’s gambling capital for a conference? The answer is “a bad week for the casino”—but you’d never guess why.
Lexie and Xavier, from Orlando, FL want to know:
“What’s going on in this video? Our science teacher claims that the pain comes from a small electrical shock, but we believe that this is due to the absorption of light. Please help us resolve this dispute!”
Even though it’s been a warm couple of months already, it’s officially summer. A delicious, science-filled way to beat the heat? Making homemade ice cream.

(We’ve since updated this article to include the science behind vegan ice cream. To learn more about ice cream science, check out The Science of Ice Cream, Redux)

Over at Physics@Home there’s an easy recipe for homemade ice cream. But what kind of milk should you use to make ice cream? And do you really need to chill the ice cream base before making it? Why do ice cream recipes always call for salt on ice?

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