The Air and What We Do To It

Five parts on an atmosphere that was swapped over, and is being swapped again. Earth's first air came out of volcanoes and was mostly carbon dioxide with essentially no oxygen, because oxygen is reactive enough that it cannot accumulate unless something keeps replacing it — and on the early Earth nothing did. Photosynthesis put the oxygen there over billions of years while the carbon went the other way, into shells, limestone and fossil fuels. The second part replaces the blanket metaphor with the mechanism: energy arrives as visible light and leaves as infrared, and only the second is absorbed. The third asks why that should be true of a trace gas when nitrogen and oxygen are ninety-nine per cent of the air, and the answer is symmetry — a molecule of two identical atoms has no lopsided vibration for an electric field to grip, while a bent carbon dioxide molecule does. The fourth opens a car exhaust and finds six products, five from the fuel and one manufactured out of the air itself by nothing but heat, which is why cleaning the fuel cannot touch it. And the last draws the whole thing as the loop it is, where burying carbon took three hundred million years and releasing it has taken two hundred.