Geoscientists at The University of Western Australia and Pennsylvania State University have found that the origins of complex life on Earth were significantly affected by volcanic activity more than two billion years ago.

They discovered that the rise of atmospheric oxygen levels, which allowed life to flourish but had long been simply attributed to ancient bacteria, was also due to terrestrial volcanic activity.

The prestigious international journal Nature has published the research paper, “Increased subaerial volcanism and the rise of atmospheric oxygen 2.5 billion years ago”.

The paper is co-authored by Professor Lee Kump, from the NASA Astrobiology Institute and Department of Geosciences at Pennsylvania State University and Professor Mark Barley, from the School of Earth and Geographical Sciences at UWA.

The paper analyses the period covering Earth’s transition from a hostile environment, where poisonous gases absorbed all the oxygen produced by the first photosynthetic organisms, to one in which oxygen levels in the atmosphere and oceans could increase and allow complex life to develop.

“We live in a unique environment.  Earth is the only planet we know of that has an oxygen-rich atmosphere, as well as a hydrosphere, and both oceanic and continental crust, which combine to sustain complex life,” Professor Barley said.

The oxygen-producing bacteria believed responsible for the rise in oxygen levels 2.5 billion years ago had been found in rocks 200 million years earlier so scientists had wondered why the bacteria had taken so long to fill the atmosphere with oxygen.

Professor Kump and Professor Barley believe the answer was that underwater volcanoes were undoing the work of the bacteria.

“We believe that the rise of atmospheric oxygen was also closely tied to the Earth’s tectonic evolution,” Professor Barley said.

The researchers analysed published studies of volcanic deposits and found a significant shift from submarine volcanoes to volcanoes on land around the same time that oxygen showed up.

“Volcanic activity produces gases that react with oxygen and remove it from the oceans and atmosphere.  Volcanoes that erupt beneath the sea produce more reduced gases than those that erupt on islands or continents and are much more effective at removing oxygen,” Professor Barley said.

As the continents thickened and stabilised, the ocean crust thinned, ocean basins could hold more water and more land bobbed above sea level.  As a result, more eruptions took place on solid ground.

The researchers found that unlike underwater volcanoes, terrestrial volcanoes soak up far less oxygen, which explains the time lag between the appearance of bacteria and oxygen’s prominence.

The shift in volcanoes allowed oxygen produced by bacteria to begin accumulating and, two billion years later, to give rise to animals.

Professor Barley said the research showed how finely balanced the Earth’s capacity for sustaining life really was.

“It is important to understand the early evolution of the Earth – we live in a time when global change is a major issue.  Human activity is increasing the amount of carbon dioxide in the atmosphere and we need to find ways to lower it, so understanding past changes may help us,” he said.

“History demonstrates that a major event can have huge implications for the planet and events can change things relatively quickly.”