Credit: © Stephen Hudson

A drawdown of oxygen into the ocean in rapidly cooling conditions could have led to the release of carbon dioxide to the atmosphere, allowing the Earth to steer clear of the tipping point into a 'snowball Earth', according to a new modelling study. This feedback loop could have acted as a buffer to control extreme temperature variations before the Cambrian explosion of life.

W. Richard Peltier from the University of Toronto1 and colleagues present a combined model of the carbon cycle and physical climate during the Neoproterozoic era, which suggests that a complete snowball state might not have occurred. The 'snowball Earth' theory proposes that for some time during the Neoproterozoic era (around 700 million years ago), the planet was entirely covered by ice. In the new model, more atmospheric oxygen is absorbed into the ocean as surface temperatures drop, which in turn mobilizes dissolved organic carbon for release into the atmosphere as carbon dioxide. The rise in atmospheric carbon dioxide levels causes warming of the Earth's surface, which counters the initial cooling effect.

During the Neoproterozoic era, conditions on Earth were clearly extreme. But the new model suggests that although the climate was unusual, the carbon cycle was even more out of kilter compared with the 635 million years that followed.