AN oxygen-rich atmosphere allowed gigantic insects to grow 300 million years
ago. Dragonflies with wingspans of up to 70 centimetres flourished in the
Carboniferous period. Researchers had long suspected that the giant insects and
lush forests needed more oxygen than the level of 21 per cent found in today’s
atmosphere.
Plants and marine life preferentially take up certain isotopes of carbon and
sulphur and their absorption changes as the concentration of oxygen rises (
Science, vol 287, p 1630). Analysis of these isotopes in ancient rocks
shows that the oxygen content of the atmosphere peaked at 35 per cent between…
