I found "aquarium cycling" to be pretty interesting. To prepare aquariums filled with water for fish, the chemistry needs to be balanced. First you put in wat

I found "aquarium cycling" to be pretty interesting. To prepare aquariums filled with water for fish, the chemistry needs to be balanced. First you put in water. Then you add drops of ammonia in the water for a few days. Somehow magically bacteria that consume ammonia and produce nitrites start populating the tank. Keep going and a second set of bacteria populate the tank, that convert nitrites to nitrates. When those bacteria are present and stable (few weeks?) the fish can be introduced to the aquarium and they will survive. There's a further step, adding plants, that can consume the nitrates (which are coincidentally in fertilizer) This article made me think of this because fish produce ammonia, and without a way for an aquarium to remove it, they will die.