The fans were the lungs of the ship. Air entered the chamber, then exited. In, out. In, out. The respiratory action was novel, but far more interesting was what happened between strokes. That was when the microorganisms did their thing.

As the air wafted through the chamber, it passed over vats of nutrient solution. Within each, colonies of tiny organisms thrived. They were cyanobacteria: among the earliest life forms on their native planet. And their numbers tinted the vats an unsettling shade of green. They were efficient, productive…ravenous. They thirsted for carbon dioxide, and their thirst was endless. 

He stared into the vats, gentle waves staining the edges. It was hard to believe anything was actually happening down there. Each organism was so tiny, yet each breath he took told him they were there. As they depended on him, he depended on them. Each provided what the other needed, and they worked together to survive in a void hostile to both. Like the cyanobacteria floating below, he was far from home. Unlike them, he understood, and in their oblivion, at times he envied them.