Are Volcanoes Behind The Oxygen We Breathe?

Earth’s early atmosphere is widely believed to be a toxic mix of carbon dioxide, nitrogen and water vapor. Then, about 2.4 billion years ago, oxygen levels began to increase exponentially. This crucial phase in Earth’s history is known as the Great Oxygenation Event (GOE) and was linked to the evolution of microorganisms capable of performing photosynthesis and splitting water into hydrogen and oxygen. A new study published by a research team from Japan describes oxygenation events predating the GOE, likely triggered by the rise of the first continents and volcanism.

“Activity of microorganisms in the ocean played a central role in the evolution of atmospheric oxygen. However, we think this would not have immediately led to atmospheric oxygenation because the amount of nutrients such as phosphate in the ocean at that time was limited, restricting activity of cyanobacteria, a group of bacteria capable of photosynthesis,” explains study coauthor Professor Eiichi Tajika from the Department of Earth and Planetary Science at the University of Tokyo.

“It likely took some massive geological events to seed the oceans with nutrients, including the growth of the continents and, as we suggest in our paper, intense volcanic activity, which we know to have occurred.”

Tajika and his team used a numerical model to simulate key aspects of biological, geological and chemical changes during the late Archean Eon (3.0 to 2.5 billion years ago) of Earth’s geologic history.

“The biggest challenge was to develop a numerical model that could simulate the complex, dynamic behavior of biogeochemical cycles under late Archean conditions. We built upon our shared experience with using similar models for other times and purposes, refining and coupling different components together to simulate the dynamic behavior of the late-Archean Earth system in the aftermath of the volatile volcanic events,” explains first author Yasuto Watanabe, a research associate at the Meteorological Research Institute in Ibaraki.

They simulated how interactions between geological features including volcanoes, plate tectonics, ocean circulation and the atmosphere created the conditions necessary for early life to oxygenate our atmosphere.

They found that large-scale volcanic activity increased atmospheric carbon dioxide, thereby warming the climate and speeding up weathering and erosion. Sediments eroded from the barren continents added minerals to the oceans, thus feeding the photosynthetic organisms, which in turn boosted their metabolism and increased atmospheric oxygen levels.

However, the increase in oxygen was not very steady, though, and came and went in bursts now known as oxygen whiffs. Likely the first free oxygen reacted with other elements, for example iron, to form sediments like Banded Ironstone Formations. Iron was eventually drained from the oceans, setting off a self-amplifying process where more and more oxygen was made available to accumulate in the atmosphere.

Between 2.4 billion and 400 million years ago, oxygen levels became high enough to sustain a more efficient metabolism based on “burning” nutrients inside cells, allowing for more complex multicellular organisms to evolve.

Today’s oxygen levels in Earth’s atmosphere are a stable balance between processes that produce oxygen — like photosynthesis by plants and microorganisms — and those that consume it — like rock weathering and oxygen-breathing organisms.

The study, “Mechanistic links between intense volcanism and the transient oxygenation of the Archean atmosphere,” was published in the journal Communications Earth & Environment.

Additional material and interviews provided by the University of Tokyo.