Oxygen

Oxygen has had extraordinary effects on life. Three hundred million years ago, in Carboniferous times, dragonflies grew as big as seagulls, with wingspans ofnearly a metre. Researchers claim they could have flown only if the air had contained more oxygen than today -probably as much as 35 per cent. Giant spiders, tree-ferns, marine rock formations and fossil charcoalsall tell the same story. High oxygen levels may also explain the global firestorm that contributed to thedemise of the dinosaurs after the asteroid impact. The strange and profound effects that oxygen has had on the evolution of life pose a riddle, which this booksets out to answer. Oxygen is a toxic gas. Divers breathing pure oxygen at depth suffer from convulsionsand lung injury. Fruit flies raised at twice normal atmospheric levels of oxygen live half as long as theirsiblings. Reactive forms of oxygen, known as free radicals, are thought to cause ageing in people. Yet ifatmospheric oxygen reached 35 per cent in the Carb