After that, you need biomass. Naturally you will have in your spice rack the complete genetic codes of all the creatures you intend to introduce into your biome. Generally you will be either recreating some Terran biome, or else mixing up something new, hybrid biomes most people call Ascensions, after Ascension Island on Earth, the site of the first such hybrid (started inadvertently by Darwin himself!) All the genomes for all the species of your particular biome will be available for print on demand, except for the bacteria involved, which are simply too numerous and too genetically labile to categorize. For them you will have to apply the appropriate inoculant, usually a muck or goo made of a few tons of the bacterial suite that you want.
Luckily bacteria grow very fast in an empty ecological niche, which is what you now have. To make it even more welcoming, scrape the interior wall of your cylinder, then crumble the rock of the scrapings finely, to a consistency ranging from large gravel to sand. Mixed with an edible aerogel, this then becomes the matrix for your soil. Put all the ice gathered in your scraping aside, except for enough when melted to make your crumbled rock matrix moist. Then add your bacterial inoculant and turn up the heat to around three hundred K. The matrix will rise like yeasted dough as it becomes that most delicious and rare substance, soil. (Those wanting a fuller explanation of how to make soil are referred to my bestselling All About Dirt.)
With a soil base cooked up, your biome is well on its way. Succession regimens at this point will vary, depending on what you are looking for at climax. But it’s true to say that a lot of terraria designers start out with a marsh of some kind, because it’s the fastest way to bulk up your soil and your overall biomass. So if you are in a hurry to occupy, this is often a good way to start.
When you’ve got a warm marsh going, either freshwater or salt, you are already cooking good. Smells will rise in your cylinder, also hydrological problems. Fish, amphibian, animal, and bird populations can be introduced at this point, and should be if you want maximum biomass growth. But here you have to watch out for a potential danger: once you get your marsh going, you may fall in love with it. Fine for you, but it happens a bit too often. We have too many estuarine biomes now, and not enough of the other biomes we are hoping to cook out here.
So try to keep your distance at this point; keep a depopulate marsh, or stay away from it during this part of the process. Or join a trading scheme in which you trade asteroids when they are at the marsh point, so that you come into a new one wanting to change things, unattached to what’s already there.
With the hefty biomass created by a marsh, you can then build up land using some of your excavated materials, saved on the surface of the asteroid for this moment. Hills and mountains look great and add texture, so be bold! This process will redirect your water into new hydrologies, and this is the best time to introduce new species, also to export species you no longer want, giving them to newer terraria that might need them.
Thus over time you can transform the interior of your terrarium to any of the 832 identified Terran biomes, or design an Ascension of your own making. (Be warned that many Ascensions fall as flat as bad souffles. The keys to a successful Ascension are so many that I have had to pen another volume, How to Mix and Match Biomes! now available.)
Ultimately you will need to make many temperature, landscape, and species adjustments, to get to the kind of stable climax community you want. Any possible landscape is achievable; sometimes the results are simply stunning. Always the entire landscape will be curving up around you, rising on both sides and meeting overhead, so that the look of the land will envelop you like a work of art-a goldsworthy inscribed on the inside of a rock, like a geode or a Faberge egg.
Obviously it is also possible to make interiors that are all liquid. Some of these aquaria or oceanaria include archipelagoes; others are entirely water, even their walls, which are sometimes refrozen transparently so that in the end when you approach them, they look like diamonds or water droplets floating in space. Some aquaria have no air space in their middles.
As for aviaries, every terrarium and most aquaria are also aviaries, stuffed with birds to their maximum carrying capacity. There are fifty billion birds on Earth, twenty billion on Mars; we in the terraria could outmatch them both combined.