Oxygen has had extraordinary effects on life. Three hundred million years ago, in Carboniferous times, dragonflies grew as big as seagulls, with wingspans of
nearly 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 charcoals
all tell the same story. High oxygen levels may also explain the...