How earth's atmosphere allowed life to evolve

Scientists may have discovered a mechanism to help determine how oxygen levels in the atmosphere expanded to allow life to evolve.

High concentrations of atmospheric oxygen have been essential for the evolution of complex life on the Earth.

Over the 4.5 billion years of Earth history, oxygen concentration has risen from trace amounts to 21 percent of the atmosphere today.

However, the mechanisms behind this rise are uncertain, and it remains one of the biggest puzzles in geochemistry.

A research group from the University of Exeter has discovered one possible mechanism, relating to the way in which carbon dioxide is removed from the atmosphere over long timescales.

"On the early Earth, CO2 levels were controlled by hydrothermal processes on the seafloor. As the Earth cooled, and the continents grew, chemical processes on the continents took over," Dr Benjamin Mills, of Geography, said.

Using computer models, the group has shown that this switch may explain increasing oxygen concentration over Earth's middle age (the Proterozoic era), which ultimately led to conditions suitable for complex life.

According to the authors, the oxygen rise is caused by a gradual increase in marine limiting nutrients, which are a product of chemical weathering of the continents.