THE explosion of complex animal life half a billion years ago may all have been down to clay.
Earth’s atmosphere has contained free oxygen since photosynthesis evolved about 2.8 billion years ago. But until sometime between a billion years ago and the start of the Cambrian period about 550 million years ago, the concentration did not rise above 0.2 per cent of modern levels, and this was nothing like enough to allow multicellular animals to evolve.
“For billions of years there was oxygen in the air, but nothing like enough to allow multicellular life to evolve”
The dramatic rise in…
