Most of life needs oxygen to thrive and science shows that O2 began to appear in the Earth’s atmosphere in severe amounts about 2.4 billion years ago. However, there was also a small injection of oxygen about 100 million years earlier, and the origin of this earlier respiration has so far been a mystery.
A new study points to volcanoes as the likely cause of this shorter oxygenation event that precedes the main one. Through an analysis of rock records, researchers have detected a corresponding increase in mercury levels indicating volcanic activity.
This activity would have led to nutrient-rich lava fields and volcanic ash, the researchers suggest, which later led to the release of these nutrients into rivers and coastal areas by weathering. This, in turn, would have allowed cyanobacteria and other unicellular organisms to flourish and begin pumping oxygen.
“Our study suggests that for these transient oxygen perfumes, the immediate trigger was an increase in oxygen production, rather than a decrease in oxygen consumption by rocks or other non-living processes,” says geologist Roger Buick of the University of Washington.
“It’s important because the presence of oxygen in the atmosphere is critical. It’s the main driver of the evolution of a large, complex life.”
Buick and colleagues examined the drilling cores extracted from the Mount McRae shale formation in Western Australia, which contained geological timelines dating back 2.5 billion years to the start of the great event. of oxygenation.
Signs of mercury enrichment and oxidation weathering convinced researchers that volcanic eruptions and the subsequent introduction of phosphorus, a key nutrient for the modulation of long-term biological activity, had played an important role in the early times of oxygen.
And although it is not clear exactly where this volcanic activity may have taken place on Earth, current geological records of locations in India and Canada, among other locations, support the hypothesis of volcanism and lava flows in the around this time.
Rock drilling cores used for analysis. (Roger Buick / University of Washington)
“During weathering under the archaic atmosphere, fresh basaltic rock would have slowly dissolved, releasing essential phosphorus from macronutrients 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 would have caused an increase in biological productivity that would have created, as a by-product, an oxygen point.”
There may have been other oxygen spikes before the Earth’s atmosphere began to really transform, but even if this study only explains one of them, it is still a bank of evidence. useful for looking at the first moments of life on our planet.
And, as with any study of this kind, there are implications for climate change research (which shows us how life adapts to less oxygen) and for space life research (which shows us the type of atmospheric conditions in which microorganisms may exist).
There are still questions about how life began on Earth in its most basic form, a billion years before the great event of oxygenation, and to answer these questions will require a better understanding of the geology of the planet through the time.
“What has begun to become obvious in recent decades is that there are a lot of connections between the non-living solid Earth and the evolution of life,” Meixnerová says.
The research has been published in PNAS.