WE ANIMALS have oxygen to thank for our very existence. For more than three billion years, microbes dominated the Earth, but after a glacial period ended 580 million years ago a surge in oxygen levels allowed multicellular animals to evolve and proliferate.
鈥淎t the end of the Gaskiers glaciation, it鈥檚 like you flicked a switch,鈥� says Guy Narbonne of Queen鈥檚 University in Kingston, Canada. The rocks change colour within a few metres, and iron compounds reveal a rapid rise in oxygen in the atmosphere to at least 15 per cent of modern levels (Science, DOI: 10.1126/science/1135013).
Narbonne thinks the big thaw triggered a boom in phytoplankton that pumped oxygen into the sea, and it quickly permeated the air. Evolution was put on fast forward and the first fossils of the flat-bodied Ediacara fauna turned up 5 million years later.
Advertisement
