Sphere

by Michael Crichton

“What happens now?” Norman said. “They pressurize us,” Ted said. “Switch us over to exotic-gas atmosphere. We can’t breathe air down here.” “Why not?” Norman said. Now that he was down here, staring at the cold steel walls of the cylinder, he wished he had stayed awake for the briefing. “Because,” Ted said, “the atmosphere of the Earth is deadly. You don’t realize it, but oxygen is a corrosive gas. It’s in the same chemical family as chlorine and fluorine, and hydrofluoric acid is the most corrosive acid known. The same quality of oxygen that makes a half-eaten apple turn brown, or makes iron rust, is incredibly destructive to the human body if exposed to too much of it. Oxygen under pressure is toxic—with a vengeance. So we cut down the amount of oxygen you breathe. You breathe twenty-one percent oxygen at the surface. Down here, you breathe two percent oxygen. But you won’t notice any difference—”