Dust devils were spinning across dry fields on the first day of our visit to the Sonoran Desert near Tucson, Ariz. That night we watched from a few feet away as hundreds of lesser long-nosed bats visited hummingbird feeders at a friend’s ranch. The species, one of 28 bat species in Arizona, feeds on nectar from saguaro cactus and other night-blooming desert flowers. On the next day flash floods and muddy back roads became the norm as the late summer “monsoon season” began in earnest. The desert landscape dominated by saguaro, the tallest cactus species in the world, is impressive, rain or shine.

Much of southern Arizona retains the charm of the natural world. The creeping sprawl of suburbia around Tucson is probably viewed as a threat by some environmentalists, but extensive ranchlands, state parks and the sheer vastness of the desert habitat itself help ensure the ecological integrity of the region. So how in the world did we manage to visit a tropical rain forest, a mangrove swamp and a small ocean while we were in the area? Welcome to Biosphere 2.

Only one biosphere on our planet has survived the test of evolutionary time. Earth’s biosphere – the global, self-contained operation of all ecosystems and life on the planet – is the product of a process that began more than 3 billion years ago. The evolutionary history of Biosphere 2 is considerably shorter. An early experiment confirmed that it does not come up to par with the real world. The original idea, conceived in the 1980s, was far ahead of its time but in keeping with the fast-developing space program. NASA had demonstrated that under the right conditions humans could survive for extended periods of time in spacecraft that orbited the earth or landed on the moon. But what about an enclosed habitat where people could live indefinitely in a self-sustaining system?

The idea that humans can populate city-size spaceships or live in colonies on other worlds is a staple of science fiction. Biosphere 2 is the leftover facility where the real-life experiment to test that idea was conducted in the early 1990s. After a series of gigantic, dome-shaped modules were constructed, representative of some of earth’s major biomes were established. The airtight system was designed so that earthlike habitats, including a small ocean with a coral reef, mangrove wetlands and a tropical rainforest, could function within a closed system. The biomes were enclosed with glass panels on 3.1 acres. In 1991 eight people were added to this biological stew with the ambitious plan of surviving in the self-contained unit. Food and oxygen were to be produced within the enormous enclosed structure while the group of scientists studied ecological changes.

A lot was learned, much unexpected, some unwanted. Roaches and an uninvited species of ants increased in alarming numbers. Most birds and pollinating insects gradually disappeared. Morning glories apparently had no natural control and began to overrun some of the forest plants. The crew is to be commended for sticking it out for almost two years, although, according to some reports, one of the participants left the facility and brought food back. Other detractors claim that oxygen levels became so low that fresh air had to be pumped into the facility. A few ecological papers based on the experience were written for scientific journals. Eventually, some insightful observations on human nature might also come from the project.

After 1994, human beings were no longer part of experiments within the facility. The current owner, the University of Arizona, began using the facility in 2007 for climate change research. Some might consider the Biosphere 2 structure that looms out of the desert as the symbol of a failed experiment on extraterrestrial colonization. And the facility may not be able to compete with the natural wonders of southern Arizona. But Biosphere 2 is certainly worth visiting. And it offers unique opportunities for research projects that can only be conducted in the world’s largest greenhouse.

Send environmental questions to ecoviews@gmail.com.

Whit Gibbons is an ecologist and environmental educator with the University of Georgia’s Savannah River Ecology Laboratory.