Steven laughed. "Keeping an ecosystem going would not be a trivial task. You can’t have actual bedrock, or a water table, or even very deep soil, at least not without major engineering challenges. So you’d have to pump water up to stream heads, and you’d have to be constantly transporting topsoil uphill to replace whatever gets washed downstream. Trees would have to be shallow-rooted. Burrowing and cave-dwelling animals would be at a disadvantage. It’s essentially like a zoo enclosure—designed to look natural, but carefully engineered nonetheless."