Volcanic mountains

Volcanic eruptions may have caused the first “puffs” of oxygen in Earth’s atmosphere – ScienceDaily


A new analysis of 2.5 billion-year-old Australian rocks reveals that volcanic eruptions may have stimulated population surges of marine microorganisms, creating the first breaths of oxygen in the atmosphere. This would change the existing stories of Earth’s early atmosphere, which assumed that most changes in the early atmosphere were controlled by geological or chemical processes.

While focused on Earth’s ancient history, the research also has implications for alien life and even climate change. The study by the University of Washington, the University of Michigan and other institutions was published in August in the Proceedings of the National Academy of Sciences.

“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,” said lead author Jana. Meixnerová, PhD student at UW in Earth and Space Sciences. “But what are the specific connections that have facilitated the evolution of life on Earth as we know it? “

In its early days, Earth had no oxygen in its atmosphere and little, if any, oxygen-breathing life forms. Earth’s atmosphere became permanently rich in oxygen around 2.4 billion years ago, possibly after an explosion of life forms that photosynthesize, turning carbon dioxide and water into oxygen.

But in 2007, Arizona State University co-author Ariel Anbar analyzed rocks in the Mount McRae shales in Western Australia, reporting a short-term breath of fresh air about 50 to 100 million years before it does not become a permanent element in the atmosphere. More recent research confirmed other earlier short-term oxygen peaks, but did not explain their rise and fall.

In the new study, researchers at the University of Michigan, led by co-corresponding author Joel Blum, analyzed the same ancient rocks for the concentration and number of neutrons in the element mercury, emitted by volcanic eruptions. . Large volcanic eruptions release mercury into the upper atmosphere, where it circulates today for a year or two before raining on the Earth’s surface. The new analysis shows a peak in mercury a few million years before the temporary increase in oxygen.

“Indeed, in the rock below the transient oxygen peak, we found evidence of mercury, both in its abundance and in its isotopes, which would most reasonably be explained by volcanic eruptions in the atmosphere,” said said co-author Roger Buick, professor at UW. Earth and Space Sciences.

Where there was volcanic emissions, the authors reason, there must have been fields of lava and volcanic ash. And these nutrient-rich rocks are said to have been weathered by wind and rain, releasing phosphorus into rivers that could fertilize nearby coastal areas, allowing oxygen-producing cyanobacteria and other single-celled life to thrive.

“There are other nutrients that modulate biological activity over short periods of time, but phosphorus is the most important over long periods,” Meixnerová said.

Today, phosphorus is abundant in biological material and in agricultural fertilizers. But in very ancient times, weathering of volcanic rocks would have been the main source of this scarce resource.

“During weathering under the Archean atmosphere, the fresh basaltic rock would have slowly dissolved, releasing essential macronutrient phosphorus in rivers. This would have fed the microbes that lived in shallow coastal areas and triggered increased biological productivity. which would have created, as a by-product, an oxygen spike, “Meixnerová said.

The precise location of these volcanoes and lava fields is unknown, but large, well-aged lava fields exist in modern India, Canada and elsewhere, Buick said.

“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 uptake by rocks or other non-living processes,” said said Buick. “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.”

Ultimately, the researchers say the study suggests how a planet’s geology might affect all life evolving on its surface, an understanding that helps identify habitable exoplanets, or planets outside of our solar system, in the search for life in the universe.

The other authors of the article are co-corresponding author Eva Stüeken, a former UW astrobiology graduate student now at St. Andrews University in Scotland; Michael Kipp, a former UW graduate student now at the California Institute of Technology; and Marcus Johnson at the University of Michigan. The study was funded by NASA, the NASA-funded UW Virtual Planetary Laboratory team, and the Blum MacArthur Chair at the University of Michigan.