How Hidden Manganese Stores Contributed to Earth’s Oxygen Generation

Deep beneath the Earth’s crust, researchers suggest that manganese may exist in a previously unidentified form. This subterranean repository could have significantly influenced the development of Earth’s oxygen-rich atmosphere.

Until around 2 billion years ago, our planet’s atmosphere was nearly devoid of oxygen. The Great Oxygenation Event (GOE)—a pivotal moment in Earth’s history—saw oxygen produced by microbial photosynthesis start to accumulate, paving the way for diverse life forms and transforming our planet.

Manganese is believed to have played a crucial role in early photosynthesis long before today’s oxygen-generating pathways evolved. Found in oxygen-rich ores, manganese began to accumulate in the Earth’s crust around the same period as the GOE.

According to Shi Jinmin from China’s Jiangsu Normal University, emerging research indicates that some of this ore may originate from as-yet-unknown manganese compounds located deep within the Earth’s mantle.

While many manganese oxides are recognized at standard pressure, Shi and his colleagues aimed to identify manganese oxides that remain stable under the extreme conditions found deep within the Earth. They utilized computer simulations to explore how various manganese and oxygen atom configurations behave at pressures up to 1.5 million times that of the Earth’s atmosphere, conditions comparable to those found nearly 2,900 kilometers below the surface.

This extensive investigation led to the discovery of several novel compounds, including ones notably rich in manganese with a ratio of four manganese atoms to every one oxygen atom. “We didn’t expect such a manganese-rich oxide to be stable across such a broad range of pressures. This was both surprising and intriguing,” Shi stated.

While the researchers lack direct evidence of these new compounds existing in the Earth’s mantle, their properties could help explain why seismic waves travel unusually slowly in certain areas where the mantle meets the core. This suggests there may be regions within the Earth’s interior that possess a high concentration of manganese, previously undetected in prior studies, Shi noted.

The newly identified manganese compounds likely migrated from the Earth’s interior to ancient ocean floors, partially explaining the surge in manganese ores during the GOE. Timothy Lyons from the University of California, Riverside, emphasizes, “[It’s] a critical aspect of the manganese cycle, influencing everything from early life evolution to modern steel and battery production and even human health.”

“This study is significant because high pressures can stabilize compounds that typically don’t exist near the Earth’s surface. Under extreme compression, atoms bond differently, resulting in unusual crystal structures and oxidation states,” remarked Caroline Peacock from the University of Leeds, UK.

However, she cautions that more evidence is required to draw definitive conclusions regarding manganese oxides in the Earth. Although the connections to seismic data, metal movements in the mantle, and the GOE are intriguing, they remain somewhat speculative.

Shi and his team aim to conduct further experiments that replicate the deep Earth conditions, employing specialized diamond equipment to achieve the necessary high pressures.