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Small compared to Earth, the completed self-contained terrarium was awesome at the human scale. Bio2 was a gigantic glass ark the size of an airport hangar. Think of an inverted ocean liner whose hull is transparent. The gigantic greenhouse was superairtight, sealed at the bottom, too, with a stainless steel tray 25 feet under the soil to prevent seepage of air from its basement. No gas, water, or matter could enter or leave the ark. It was a stadium-size Ecosphere -- a big materially closed and energetically open system -- but far more complex. Bio2 was the second only to Biosphere 1 (the Earth) as largest closed vivisystem.

The challenge of creating a living system of any size is daunting. Creating a living wonder at the scale of Bio2 could only be described as an experiment in sustained chaos. The challenge included: Select a couple of thousand parts of out of several billion possibilities, and arrange them so that all the parts complemented and provided for each other, so that the whole mixture was self-sustaining over time, and that no single organism became dominant at the expense of others, so that the whole aggregate kept all the constituents in constant motion, without letting any ingredient become sequestered off to the side, while keeping the entire level of activity and atmospheric gases elevated at the point of perpetually almost-falling. Oh, and humans should be able to live, eat, and drink within and from it.

SBV decided to stake the survival of Bio2 on the design tenet that an extraordinarily diverse hodgepodge of living creatures would settle into a unified stability. If it proved nothing else, the experiment would at least shed some light on the almost universally held assumption in the last two decades: that diversity ensures stability. It would also test whether a certain level of complexity birthed self-sustainability.

As an architecture of maximum diversity, the final Bio2 floor plan had seven biomes (biogeographical habitats). Under the tallest part of the glass canopy, a rock-faced concrete mountain bulged. Planted with transplanted tropical trees and a misting system, the synthetic hill was transformed into a cloud forest -- a high altitude rain forest. The cloud forest drained into an elevated hot grassland (the size of a big patio, but stocked with waist-high wild grasses). One edge of the rain forest stopped before a rocky cliff which fell to a saltwater lagoon, complete with coral, colorful fishes, and lobsters. The high savanna lowered into a lower, drier savanna, dark with thorny, tangled thickets. This biome is called thornscrub and is one of the most common of all habitats on Earth. In real life it is nearly impenetrable to humans (and thus ignored), but in Bio2, it served as a little hideaway for both wildlife and humans. The thicket leads into a compact marshy wetland, the fifth biome, which finally emptied into the lagoon. The low end of Bio2 was a desert, as big as a gymnasium. Since it was pretty humid inside, the desert was planted with fog desert plants from Baja California and South America. Off to one side was the seventh biome -- an intensive agriculture and urban area where eight Homo sapiens grew all their own food. Like Noah's place, animals were aboard; some for meat, some for pets, and some on the loose: lizards, fish, birds roaming about the wild parts. There were honey bees, papaya trees, a beach, cable TV, a library, a gym, and a laundromat. Utopia!

The scale was stupendous. Once while I was visiting the construction site, an 18-wheeler semi-truck pulled up to the Bio2 office. The truck driver leaned out the window and asked where they wanted their ocean. He'd been hauling a full truckload of ocean salt and needed to unload it before dark. The office clerks pointed down to a very large hole in the center of the project. That's where Walter Adey from the Smithsonian Institution was building a one-million-gallon ocean, coral reef, and lagoon. There was enough elbow room in this gargantuan aquarium for all kinds of surprises to emerge.

Making an ocean is no cinch. Ask Gomez and the hobby saltwater aquarists. Adey had grown an artificial self-regenerating coral reef once before as a museum exhibit at the Smithsonian. But this one in Bio2 was huge; it had its own sandy beach. An expensive wave-making pump at one end would supply the turbulence coral love. The same machine created a half-meter tide on a lunar cycle.

The trucker unloaded the ocean: stacks of 50-pound bags of Instant-Ocean, the same stuff you buy at tropical aquarium stores. A starter solution harboring all the right microbeasties (sort of the yeast for the dough) was later hauled in on a different truck from the Pacific Ocean. Stir together well, and pour.

The ecologists building the wilderness areas of Bio2 were of the school that says: soil + bugs = ecology. To have the kind of tropical rainforest you want, you needed to have the right kind of jungle dirt. And to get that in Arizona you had to make it from scratch. Take a couple of bulldozer buckets of basalt, a few of sand, and a few of clay. Sprinkle in the right microorganisms. Mix in place. The underlying soils in each of the six wild biomes of Bio2 were manufactured in this painstaking way. "The thing we didn't realize at first," said Tony Burgess, "was that soils are alive. They breathe as fast as you do. You have to treat soil as a living organism. Ultimately it controls the biota."

Once you have soil, you can play Noah. Noah rounded up everything that moved for his ark, but that certainly wasn't going to work here. The designers of the Bio2 closed-system kept coming back to that most exasperating but thrilling question: what species should Bio2 include? No longer was it merely "Which organisms do we need to mirror the breath of eight humans?" The dilemma was "Which organisms do we need to mirror Gaia? Which combination of species would produce oxygen to breathe, plants to eat, plants to feed the animals to eat (if any), and species to support the food plants? How do we weave a self-supporting network out of random organisms? How do we launch a coevolutionary circuit?"

Take almost any creature as an example. Most fruit requires insects to pollinate it. So if you wanted blueberries in Bio2, you needed honeybees. But in order to have honeybees around when the blueberries are ready for pollination, you needed to provide the honeybees with flowers for the rest of the season. But in order to supply sufficient seasonal flowers to keep honeybees alive, there would be no room for other kinds of plants. So, perhaps another type of pollinating bee would work? You could use straw bees which can be supported with meager amounts of flowers, but they don't pollinate blueberry blossoms or several other fruits you wanted. How about moths? And so on down the catalog of living creatures. Termites are necessary to decompose old woody vegetation, but they were fond of eating the sealant around the windows. What's a benign termite substitute that would get along with the rest of the crowd?

"It's a sticky problem," said Peter Warshall, a consulting ecologist for the project. "It's a pretty impossible job to pick 100 living things, even from the same place, and put them together to make a 'wilderness'. And here we're taking them from all over the world to mix together since we have so many biomes."

To cobble together a synthetic biome, the half-dozen Bio2 ecologists sat down at a table together and played this ultimate jigsaw puzzle. Each scientist had expertise in either mammals, insects, birds, or plants. But while they knew something about sedges and pond frogs, very little of their knowledge was systematically accessible. Warshall sighed, "It would have been nice if somewhere there was a database of all known species listing their food and energy requirements, their habitat, their waste products, their companion species, their breeding needs, etc., but there isn't anything remotely like that. We know very little about even common species. In fact, what this project shows is how little we know about any species."

The burning question for the summer the biomes were designed was "Well, how many moths does a bat really eat?" In the end, selecting the thousand or so higher species came down to informed guesses and biodiplomacy. Each ecologist wrote up a long lists of possible candidates, including favorite species they thought would be the most versatile and flexible. Their heads were full of conflicting factors -- pluses and minuses, likes to be near this guy but can't stand this one. The ecologists projected the competitiveness of rival organisms. They bickered for water or sunlight rights. It was if they were ambassadors protecting the territory of their species from encroachments.

"I needed as much fruit as possible dropped from trees for my turtles to eat," said Bio2 desert ecologist Tony Burgess, "but the turtles would leave none for the fruit flies to breed on, which Warshall's hummingbirds needed to eat. Should we have more trees for leftover fruit, or use the space for bat habitat?"

So negotiations take place: If I can have this flower for the birds, you can keep the bats. Occasionally the polite diplomacy reverted to open subversion. The marsh-man wanted his pick of sawgrass, but Warshall didn't like his choice because he felt the species was too aggressive and would invade the dry land biome he was overseeing. In the end Warshall capitulated to the marsh-man's choice, but added, half in jest, "Oh, it doesn't make any difference because I'm just gonna plant taller elephant grass to shade out your stuff, anyway." The marsh-man retaliated by saying he was planting pine trees, taller than either. Warshall promised with a hearty laugh to plant a defense border of guava trees, which don't grow any taller, but grow much faster, staking out the niche early.

Everything was connected to everything. It made planning a nightmare. One approach the ecologists favored was building redundancy of pathways into the food webs. With multiple foodchains in every web, if the sand flies died off, then something else became second choice food for the lizards. Rather than fight the dense tangle of interrelationships, they exploited them. The key was to find organisms with as many alternative roles as possible, so that if one didn't work out, it had another way or two to complete somebody's loop.

"Designing a biome was an opportunity to think like God," recalled Warshall. You, as a god, could create something by nothing. You could create something -- some wonderful synthetic vibrant ecosystem -- but you had no control over precisely what something emerged. All you could do was gather all the parts and let them self-assemble into something that worked. Walter Adey said, "Ecosystems in the wild are made up of patches. You inject as many species as you can into the system and let it decide what patch of species it wants to be in." Surrendering control became one of the "Principles of Synthetic Ecology." Adey continued, "We have to accept the fact that the amount of information contained in an ecosystem far exceeds the amount contained in our heads. We are going to fail if we only try things we can control and understand." The exact details of an emerging Bio2 ecology, he warned, were beyond predicting.

But details counted. Eight human lives rested on the details fusing into a whole. Tony Burgess, one of the Bio2 gods, ordered dune sand to be trucked in for the desert biome because construction sand, the only kind on hand at the Bio2 site, was too sharp for the land turtles; it cut their feet. "You've got to take care of your turtles, so they can take care of you," he said in a priestly way.

The number of free-roaming animals taking care of the system was pretty thin for the first two years in Bio2 because there wasn't enough wild food to support very many of them. Warshall almost didn't put any monkeylike galagos from Africa in because he wasn't sure the young acacia trees could produce enough gum to satisfy them. In the end he released four galagos and stored a couple hundred pounds of emergency monkeychow in the basement of the ark. Other wild animal occupants of Bio2 included leopard tortoises, blue-tongued skinks ("because they are generalists" -- not picky what they eat), various lizards, small finches, and pygmy green hummingbirds, partially for pollination. "Most of the species will be pygmy," Warshall told a Discover reporter before closure, "because we really don't have that much space. In fact, ideally we'd have pygmy people, too."

The animals didn't go in two by two. "You want to have a higher ratio of females to males for reproduction insurance," Warshall told me. "Ideally we like to have at minimum five females per three males. I know director John Allen says that eight humans -- four female, four male -- is the minimum-size group needed for human colony start-up and reproduction, but from an ecologically correct rather than politically correct point of view, the Bio2 crew should be five females and three males."

For the first time biologists were being forced by the riddle of creating a biosphere to think like engineers: "Here is what we need, what materials will do that job?" At the same time, the engineers on the project were being forced to think like biologists: "That's not dirt, that's a living organism!"

A stubborn problem for the designers of Bio2 was making rain for the cloud forest. Rain is hard. The original plans optimistically called for cooling coils at the peak of the 85-foot glass roof over the jungle section. The coils would condense the jungle's moisture into gentle drops descending from the celestial heights -- real artificial rain. Early tests proved the drops to be scarce, too large and destructive when they landed, and not at all the constant gentle mist the plants wanted. Second plan was for the rain to be pumped up into sprinklers bolted to the frame structure high overhead, but that proved to be a maintenance nightmare since over a two-year period the fine-holed mist heads were sure to need unclogging or replacements. The design they ended up with was "rain" squirted from misting nozzles fitted on the ends of pipes stationed here and there on the slopes.

One unexpected consequence of living in a small materially closed system is that rather than water becoming precious, it's in virtual abundance. In about one week 100 percent of the water is recycled, cleansed by microbiological activity in wetland treatment areas. When you use more water, it just goes around the loop a little faster.

Any field of life is a cloth woven with countless separate loops. The loops of life -- the routes which materials, functions, and energy follow -- double up, cross over and interweave as knots until it is impossible to tell one thread from another. Only the larger pattern knitted by the loops emerges. Each circle strengthens the others, until the whole is hard to unravel.

That is not to say there will be no extinctions in a tightly wrapped ecosystem. A certain extinction rate is essential for evolution. Walter Adey had about 1 percent attrition rate in his previous partially closed coral reef. He expected about a 30 to 40 percent drop-off in species within the whole of Bio2 by the end of its first two-year run. (The biologists from Yale University who are currently counting the species after reopening have not finished their studies of species attrition as of my writing).

But Adey believes that he already has learned how to grow diversity: "What we are doing is cramming more species in than we expect to survive. So the numbers drop. Particularly the insects and lower organisms. Then, at the beginning of the next run we overstock it again, injecting slightly different species -- our second guesses. What will probably happen is that there will still be a large loss again, maybe one quarter, but we reinject again next closure. Each time the numbers of species will stabilize at a higher level than the first. The more complex the system, the more species it can hold. We keep doing that, building up the diversity. If you loaded up Biosphere 2 with all the species it ends up with, it would collapse at the start." The huge glass bottle is a diversity pump that grows complexity.

The Bio2 ecologists were left with the large question of how best to jump start the initial variety, upon which further diverse growth would be leveraged. This was very much related to the practical problem of how to load all the animals onto the ark. How do you get 3,000 interdependent creatures into a cage, alive? Adey proposed moving an entire natural biome into Bio2's relatively miniature space by compressing it in the manner of a condensed book: selecting choice highlights here and there, and fusing these bits into a sampler.

He selected a fine 30-mile stretch of a Florida Everglade mangrove swamp and had it surveyed into a grid. Every half mile or so along the salt gradient, a small cube (4-feet deep by 4-feet square) of mangrove roots was dug out. The block of leafy branches, roots, mud, and piggybacking barnacles was boxed and hauled ashore. The segments of the marsh, each one tuned to a slightly different salt content with slightly different microorganisms, were trucked to Arizona (after long negotiations with very confused agricultural custom agents who thought "mangroves" were "mangoes").

While the chunks of everglades were waiting to be placed in the Bio2 marsh, the Bio2 workers hooked the watertight boxes up into a network of pipes so that they became one distributed saltwater tide. Later the 30 or so cubes were reassembled into Bio2. Unboxed, the reconstituted marsh takes up only a micro 90-by-30 feet. But within this volleyball court-size everglade, each section harbors a gradually increasing salt-loving mixture of microorganisms. Thus, the flow of life from freshwater to brine is compressed into talking distance. The problem with the analog method is that scale is an important dimension of an ecosystem. As Warshall juggled the parts to manufacture a miniature savanna, he shook his head: "At best we are putting about one-tenth the variety of a system into Bio2. For the insect population it's more like one-hundredth. In a West African savanna there are 35 species of worms. At most we'll have three kinds. So the dilemma is: are we making a savanna or a lawn? It's surely better than a lawn...but how much better I don't know."