For nearly 90% of Earth’s history, our planet’s atmosphere contained almost no oxygen, making it completely uninhabitable for humans and most modern life forms. Then, around 2.5 billion years ago, something remarkable happened: Earth’s atmosphere began to fill with oxygen in what scientists call the Great Oxidation Event (GOE). This atmospheric revolution changed our planet’s chemistry and paved the way for complex life.
But this wasn’t a sudden change. Before the GOE, Earth’s atmosphere occasionally experienced temporary “whiffs” of oxygen—mysterious spikes that came and went. What caused these oxygen previews has puzzled scientists for years. Now, researchers from the university of Tokyo have found a surprising answer: massive volcanic eruptions.
Volcanoes: Unlikely oxygen producers
In a study published in Communications Earth & Environment, scientists showed how enormous volcanic eruptions known as Large Igneous Provinces (LIPs) could have triggered these temporary oxygen events. Their computer models revealed that intense volcanic periods could have caused oxygen increases lasting several million years.
But how could volcanoes, which release carbon dioxide and other gases, lead to more oxygen? The answer involves a chain reaction through Earth’s early systems.
When these enormous eruptions occurred, they released vast amounts of carbon dioxide, warming the planet. This warming increased the breakdown of continental rocks, releasing phosphorus into the oceans. This phosphorus fed photosynthesizing microbes, which produced oxygen as a byproduct.
“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,” says professor Eiichi Tajika from the University of Tokyo, in a statement. “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.”
Ancient rocks tell the tale
These findings explain puzzling evidence found in rocks like the Mt. McRae Shale in Australia. Deposited around 2.5 billion years ago, this rock contains elevated levels of elements like molybdenum and rhenium, which point to a temporary oxygen increase. This oxygen spike would have lasted between several million to 11 million years, matching what the models predict.
The evidence for these oxygen whiffs isn’t limited to one location. The original research paper notes that the whiff event recorded in Mt. McRae Shale coincided with redox-sensitive element enrichment in the Klein Naute Formation in South Africa. This suggests these oxygen increases may have been widespread phenomena rather than isolated local events.
This makes sense based on our understanding of how Earth’s surface was evolving at this time. The late Archean period was a time of significant planetary change. Continents were growing, volcanic activity was reshaping the surface, and life was evolving new metabolic capabilities.
“Understanding the whiffs is critical for constraining the timing of the emergence of photosynthetic microorganisms,” says visiting research associate 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.”
The continental connection
The study suggests that as continents grew larger during the late Archean period (about 3.5 to 2.5 billion years ago), Earth became more susceptible to these oxygen whiffs. With more land surface, more phosphorus and other nutrients could potentially be weathered and washed into the oceans, amplifying the effect of volcanic eruptions.
The researchers’ models indicate that when continents were small, even massive volcanic eruptions might not have triggered significant oxygen whiffs. But as continents grew, the same-sized eruption could produce a much larger oxygen response.
The researchers tested this idea by running their model with different continental sizes and volcanic inputs. With small continental areas, atmospheric carbon dioxide levels would increase dramatically after an eruption (to around 500 times present levels), but marine nutrient concentrations would barely change. This limited nutrient availability meant photosynthetic oxygen production stayed low.
However, as continental area increased in the model, the same volcanic eruption led to significant increases in marine nutrients and oxygen production. This pattern might help explain why oxygen whiffs seem to have become more common in the late Archean, just before the Great Oxidation Event.
Evolutionary pressures and modern implications
These periodic oxygen previews may have created conditions for early life forms to develop oxygen-processing abilities long before oxygen became a permanent feature of Earth’s atmosphere. These temporary spikes could have created evolutionary pressure for microorganisms to develop mechanisms for dealing with oxygen. The ability to detoxify oxygen or use it metabolically would later become advantageous when oxygen became permanently abundant in the atmosphere.
Each volcanic eruption that triggered an oxygen whiff may have pushed Earth’s system closer to the tipping point for permanent oxygenation. Ancient volcanoes’ fiery eruptions billions of years ago might have helped set the stage for the oxygen-filled atmosphere we all depend on today.
Source : https://studyfinds.org/earths-first-oxygen-surge-volcanic/