Biosphere 2 Is the Largest Closed System Ever Made

Biosphere 2 Is the Largest Closed System Ever Made

Learn what happened when people tried to live inside it.

Perhaps the most ambitious (certainly the largest) closed ecosystem humans have ever conceived is Biosphere 2, a 3.14-acre Earth system research complex located in the desert outside of Tuscon, Arizona. Built in the early ’90s by the now-defunct company Space Biosphere Ventures, this massive glass and metal greenhouse complex, filled with representative “biomes” from across the planet, was intended to serve as a simulation for future space habitats. It was constructed as a materially closed system, meaning there was no exchange of atmosphere or water with the outside world, only sunlight.

A Biosphere 2 living experiment began in 1991, when eight men and women sealed themselves inside the complex with nothing but simple tools. The plan was to grow all of their own food and survive off the land for as long as possible. It was an unmitigated train wreck.

The initial idea behind Biosphere 2 was that a self-sustaining, closed system that mimicked the environments of Earth would be a necessity once humans began colonizing other planets. The project began in 1987, and ended up as the largest closed system ever created, spanning more than 3 acres and containing 5 distinct biomes. Though two attempts at having teams live inside the project ultimately failed, Biosphere 2 remains the world’s largest earth sciences lab. Its miniature ecosystems continue to thrive and provide valuable data, and some of the experiments occurring within are geared toward the project’s first mission: bringing a bit of Earth into space.

Throughout the two years that the living experiment lasted, CO2 levels within the habitat fluctuated by as much as 600 parts per million every day, thanks to the drawdown of carbon during sunlight hours by photosynthesis, and its subsequent release at night through plant metabolism. (The concentration of CO2 in Earth’s atmosphere today is just north of 400 ppm). CO2 also varied seasonally with light availability, reaching peak concentrations of 4500 ppm in the winter and 1000 ppm in the summer. Most of the complex’s vertebrate life and pollinating insects died, while populations of greenhouse ants and cockroaches exploded. Morning glories threatened to choke out all other plants. Filtrations systems clogged, and unexpected condensation made the desert soggy.

Worst, oxygen concentrations in the facility fell steadily, from a healthy 20 per cent at the outset to 14.5 per cent at 16 months in — roughly equivalent to oxygen levels at an altitude of 13,400 feet. When the half-starved Biospherians began suffering from sleep apnea and chronic fatigue, the management group decided to intervene and artificially boost the O2.

The reason for the oxygen shortage was unclear at the time, but later studies would demonstrate that the culprit was probably decomposer microorganisms in the soil. When the Biospherians built the system, they included the most organic-rich soils possible to give the plants their best chance at survival. But the fertile soils also harboured large populations of oxygen-consuming microbes. This issue — and many of the experiment’s other problems — might have been prevented had the system been designed with greater scientific oversight.

And yet, the efforts of the intrepid humans who sealed themselves inside Biosphere 2 weren’t a total waste, because we learned an awful lot. Biosphere 2’s failure became an important cautionary tale, underscoring how easily closed ecosystems can spiral out of control if the initial conditions of the system are not carefully measured and aligned. (After more than a decade of inactivity, the facility was acquired by the University of Arizona in 2007, and has since been repurposed as a state-of-the-art Earth science laboratory).

Watch: Inside Biosphere 2: The World’s Largest Earth Science Experiment

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