Earth's oxygen supply may have been kick-started by volcanoes

When you take a deep breath, have you ever considered the composition of the air filling your lungs? Oxygen makes up only 21%, while nitrogen dominates. But this ratio has not always been constant. Throughout Earth’s history, oxygen levels have fluctuated, sometimes drastically, leading to mass extinctions and evolutionary shifts.

Scientists believe Earth’s atmosphere became rich in oxygen about 2.5 billion years ago due to photosynthetic microorganisms. However, new research suggests volcanic activity may have played a crucial role in setting the stage for this transformation.

A team of scientists led by the University of Tokyo proposes that volcanic eruptions influenced precursor oxygenation events, or “whiffs,” that signaled the coming Great Oxygenation Event (GOE).

Role of microbes in oxygenation

The GOE marked a significant increase in atmospheric oxygen, enabling the rise of complex life. The prevailing theory suggests that a surge in microorganisms capable of photosynthesis converted the carbon dioxide-rich atmosphere into one dominated by oxygen.

But before the GOE, smaller oxygenation events occurred, hinting at earlier environmental shifts that made oxygenation possible.

“Activity of microorganisms in the ocean played a central role in the evolution of atmospheric oxygen,” said Professor Eiichi Tajika from the Department of Earth and Planetary Science at the University of Tokyo.

“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.”

“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.”

Large igneous provinces and their impact

The new study highlights the influence of large igneous provinces (LIPs), massive volcanic regions formed by intense eruptions. The researchers used a biogeochemical model to analyze how these eruptions altered Earth’s atmosphere.

They found that volcanic activity increased atmospheric carbon dioxide, warming the climate and supplying nutrients to the ocean. This, in turn, boosted marine productivity and triggered short-lived increases in atmospheric oxygen.

These whiffs lasted for several million years, suggesting that volcanic events repeatedly caused temporary atmospheric oxygenation before the GOE.

However, as continents expanded, they reduced the likelihood of these transient events by stabilizing conditions. The study suggests that these whiffs indicate Earth was approaching a tipping point, leading to the permanent rise of atmospheric oxygen.

Signs of early oxygen bursts on Earth

“Understanding the whiffs is critical for constraining the timing of the emergence of photosynthetic microorganisms. The occurrences are inferred from concentrations of elements sensitive to atmospheric oxygen levels in the geologic record,” said study lead author Yasuto Watanabe.

“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.”

The team examined redox-sensitive elements such as molybdenum, rhenium, and selenium, which indicate oxidative weathering of continental minerals. One well-documented whiff occurred around 2.5 billion years ago and is recorded in the Mt. McRae Shale in Australia.

These findings, along with isotopic data, support the idea that transient oxygenation events were linked to volcanic activity.

Linking volcanism to oxygenation

Volcanic eruptions release large amounts of carbon dioxide and other greenhouse gases, leading to warming and increased weathering of rocks.

This process delivers nutrients like phosphate to the ocean, fueling microbial activity. As these microorganisms thrived, they produced oxygen, leading to brief atmospheric oxygenation.

However, once the nutrient supply declined, oxygen levels dropped again. This cycle repeated until the GOE, when atmospheric conditions finally stabilized at higher oxygen levels.

The model suggests that whiffs were a key step in the Earth system’s transition from a reducing to an oxidizing atmosphere.

Short oxygen bursts led to Earth’s air

These findings suggest that Earth’s atmosphere did not change in a single event but rather through a series of oxygenation episodes driven by geological and biological interactions.

The rise of oxygen-utilizing enzymes before the GOE supports the idea that life was already adapting to these transient oxygen-rich periods.

By linking large-scale volcanic activity to early atmospheric oxygenation, this research provides a clearer picture of how Earth evolved into the habitable planet it is today.

It also reinforces the idea that planetary-scale changes, driven by both internal and external factors, shaped the conditions necessary for complex life to emerge.

The study is published in the journal Communications Earth & Environment.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–