Ancient mineral particles may have fuelled the rise of Earth's oxygen

Up to now, scientists have maintained that the oxygen (O₂) increase in the Earth's atmosphere billions of years ago resulted from photosynthesis by marine plants and algae. 

However, according to a study published in Nature Geoscience on March 6, photosynthesis does not fully account for the rise in O₂ levels. Instead, mineral particles played a crucial role significantly impacting how intelligent life evolved.

The research offers a new understanding of how O₂ became abundant in Earth's atmosphere and provides a glimpse into the conditions needed for complex life to develop in distant worlds. 

Where does Earth's oxygen come from?

Researchers from the University of Leeds argue that as the algae and plants perished, they would have been eaten by microorganisms. This process, known as decomposition, depletes the atmosphere of O₂. 

Assuming the total atmospheric O₂ is a balance between this depletion and photosynthesis (where O₂ is gained), the researchers believe the former process must have been reduced or stopped for its levels to rise.

They claim that this was made possible by a process known as mineral-organic carbon preservation. Simply put, this happens when iron-containing minerals from the oceans attach to dead algae and plants, preventing them from decomposing. The overall outcome allowed O₂ levels to rise unrestricted.

 "Scientists have known for many years that mineral particles can bind with dead algae and plants...shielding them from the decay process," said lead author Professor Caroline Peacock in a press release.

"But whether mineral particles helped fuel the rise of atmospheric oxygen had never been tested," she explained.  

The group got to work evaluating their hypothesis against well-known geological occurrences where mineral particle concentrations were likely higher. 

For instance, the atmosphere's oxygen content increased during the Great Oxidation Event 2.4 billion years ago. This was at the same time as the continents were gradually forming, which would have increased the number of mineral particles that flowed into the oceans.

"The increase in mineral particles in the oceans would have reduced the rate at which algae was being decomposed. This had a major impact on oxygen levels, allowing them to rise," explained Dr. Mingyu Zhao, who performed the study.

He highlighted that the rise of atmospheric oxygen significantly impacted the emergence of life. It led to the emergence of more complex species that transitioned from living in the water to living on land. 

The complete study was published in Nature Geoscience on March 6 and can be found here.