New research reveals Earth’s ancient ‘breathing’

Tiny mineral inclusions show for the first time the accumulation of oxygen in the atmosphere and the change of mantle composition. Credit: Hugo Moreira / Natural Geosciences

Researchers have identified a link between ancient atmospheric shifts and the chemistry of Earth’s mantle, which sheds light on the evolution of the planet.

An international team of scientists has discovered an important link between Earth’s early atmosphere and the chemistry of its deep mantle.

Led by researchers at University of Portsmouth The study, conducted by the University of Montpellier, sheds new light on the evolution of life on our planet and the rise in oxygen in the atmosphere.

Exploration of the Great Oxidation Event

The team investigated magma that formed at ancient subduction zones, where parts of the Earth’s crust sink back into the mantle, from a pivotal moment in Earth’s history – the Great Oxidation Event (GOE). This event, which is estimated to have occurred between 2.1 and 2.4 billion years ago, was a time period in which oxygen levels in the Earth’s atmosphere increased rapidly and transformed life and environments on Earth.

However, there has been little research on how atmospheric changes leave their mark on the Earth’s mantle.

Graph showing changes in weather conditions. Credit: Dr. Hugo Moreira

Tectonic processes and the Earth’s mantle

The new study published in the journal Natural Earth SciencesHe studied the role of plate tectonics – the process by which our planet’s outer crust moves and reshapes its surface – in the circulation and exchange of elements between the atmosphere, Earth’s surface and the deep mantle. Until now, reliable ways to understand these interactions have been elusive.

By studying magmas before and after GOE, the team found a shift from low-lying magmas to more oxidized magmas. This was the result of the deep subduction of oxidised sediments from mountains that were transformed into sediments during weathering and erosion, which were then recycled into the mantle via subduction processes – revealing how sediment recycling provided access to the mantle atmosphere.

Low apatite inclusions. Credit: Dr. Hugo Moreira

The importance of discovery

This discovery indicates that these oxygen ‘squirts’ may have altered the mantle by contributing to increased oxidation of calcareous-alkaline magmas, altering the composition of the continental crust, and leading to the formation of ore deposits on Earth.

Lead author, Dr Hugo Moreira from the University of Montpellier and a visiting researcher at the University of Portsmouth, said: “With these findings, our understanding of the ancient ‘breathing’ of the Earth has taken a huge leap forward. Not only does it provide important insights into the Earth’s geological evolution, but it also sheds light on how the Earth’s depths and mantle are intimately linked to atmospheric changes. It gives us a better understanding of the relationship between Earth’s external and internal reservoirs.

“Moreover, it raises fascinating questions about the role oxygen has played in shaping our planet’s history and the conditions that paved the way for life as we know it.”

Oxidized apatite inclusions. Credit: Dr. Hugo Moreira

Research Methodology

The research team used the ID21 beamline at the European Synchrotron Radiation Facility in France to analyze the sulfur state of the minerals in two-billion-year-old zircon crystals from Brazil’s Mineiro belt, which served as time capsules, while preserving their original composition. . They discovered that the minerals in the magma that crystallized before the gas erupted had a low sulfur state. However, after the Egyptian government, these became more oxidized.

European Synchrotron Radiation Facility. Credit: European Synchrotron Radiation Facility

Conclusion

Dr Moreira said: “Mantle oxygen demise is, in simple terms, a measure of oxygen’s ability to catalyze chemical reactions in magma, which is critical to understanding volcanic activity and ore formation. However, in the past, we lacked a reliable way to track changes in this parameter for older parts of Earth’s history – until now.

“It provides a powerful tool for understanding the relationship between Earth’s external and internal reservoirs. Sulfur species and magma velocity are dynamic factors that can change throughout a magma’s journey from formation to crystallization. While our study took into account factors such as pressure and temperature, further analyzes are needed.” to trace the entire ‘fragility pathway’ from magma generation to final crystallization.

Co-author Professor Craig Storey, Professor of Geology at the University of Portsmouth, said: “Our study opens exciting new avenues for research, providing a deeper understanding of Earth’s ancient past and its deep connection to the evolution of our atmosphere. It challenges us to ponder questions about the evolution of magma types over time and the complex interaction of plate tectonics. and atmospheric cycles.

Dr Moreira added: “As we continue to explore the mysteries of Earth’s geological history, one thing is certain, and that is that there is much more to be discovered beneath the surface.”

For more information on this research, see Unlocking the Mysteries of Earth’s Ancient Atmosphere.

Reference: “Subarc mantle demise transformed by sediment recycling 1 via the Great Oxidation Event” by Hugo Moreira, Craig Storey, Emily Broand, James Darling, Mike Fowler, Marin Kott, Edgar E. Villalobos-Portillo, Flores Barat, Luis Seixas, Pascal Filippou and Bruno Duem, August 31, 2023, Natural Earth Sciences.
doi: 10.1038/s41561-023-01258-4

Researchers from the University of Portsmouth, the Universities of Brest and Montpellier, the Sorbonne University (France), the Federal University of Ouro Preto and the University of São Paulo (Brazil) and the European Synchrotron Radiation Facility (ESF) participated in the study.