Volcanoes could be responsible for the first breaths of oxygen on Earth

Most life needs oxygen to thrive, and science shows that O₂ began to appear in the Earth’s atmosphere in significant quantities some 2.4 billion years ago. However, there was also a small injection of oxygen around 100 million years earlier than that – and the origin of this earlier breathing has so far been a mystery.

A new study indicates that volcanoes are the likely cause of this shorter preceding oxygenation event. Through an analysis of the rock records, the researchers spotted a corresponding increase in mercury levels that indicates volcanic activity.

This activity would have led to fields of lava and volcanic ash rich in nutrients, suggest the researchers, which then led to the release of these nutrients in rivers and coastal areas by inclement weather. That, in turn, would have allowed cyanobacteria and other single-celled organisms to thrive – and start pumping oxygen.

“Our study suggests that for these transient bursts of oxygen, the immediate trigger was an increase in oxygen production, rather than a decrease in oxygen consumption by rocks or other non-living processes,” explains geologist Roger Buick of the University of Washington.

“This is important because the presence of oxygen in the atmosphere is fundamental – it is the main driver of the evolution of a vast and complex life.”

Buick and colleagues examined drill core taken from the Mount McRae shale formation in Western Australia, containing geological timelines dating back 2.5 billion years before the start of the Great Oxygenation Event.

Signs of mercury enrichment and oxidative weathering convinced researchers that volcanic eruptions and the subsequent introduction of phosphorus – a key nutrient to modulate biological activity over long periods of time – had played a major role in the early oxygen peak.

And although it is not known exactly where on Earth this volcanic activity could have taken place, geological records from places in modern India and Canada, among others, confirm the hypothesis of volcanism and lava flows at that time.

Rock drill cores used for analysis. (Roger Buick / University of Washington)

“During weathering under the Archean atmosphere, the fresh basaltic rock would slowly dissolve, releasing essential macronutrient phosphorus into rivers,” says astrobiologist Jana Meixnerová of the University of Washington.

“This would have fed the microbes that lived in the shallow coastal areas and triggered increased biological productivity which would have created, as a by-product, a spike in oxygen.”

There may well have been other oxygen peaks before Earth’s atmosphere began to seriously transform, but even though this study only explains one of them, it does. always acts as a bank of evidence useful for diving back into the first moments of life on our planet.

And as with any such study, there are implications for both climate change research (showing us how life adapts to less oxygen) and the search for life in space (showing us the type of atmospheric conditions in which microorganisms may exist).

Questions remain about how life on Earth began in its most basic form, a billion years before the Great Oxygenation Event, and answering these questions will require a better understanding of the geology of the planet across the weather.

“What has started to become evident over the past few decades is that there are actually a number of connections between solid and non-living Earth and the evolution of life,” Meixnerová explains.

The research was published in PNAS.