Discovery: bacteria were breathing oxygen 1 billion years before the Great Oxidation 🫧

Microbial life on Earth still holds surprises. A recent study overturns our certainties about the emergence of oxygen respiration, revealing an adaptation much earlier than previously estimated.


This discovery is based on innovative genomic and geochemical analysis. It suggests that certain bacteria were already exploiting oxygen over 3 billion years ago, long before the Great Oxidation that transformed Earth's atmosphere.

Oxygen, an unexpected metabolic advantage

Until now, scientists believed that aerobic respiration (using oxygen as fuel) did not exist before the Great Oxidation, which occurred 2.4 billion years ago. The study demonstrates that ancestral bacteria were using this gas nearly a billion years earlier.

These pioneering microorganisms likely took advantage of local oxygenated niches, such as coastal areas or hydrothermal vents. Their ability to metabolize oxygen would have favored their survival and diversification.

This early adaptation challenges the classic timeline of microbial evolution. It indicates that oxygen, though scarce, already played a key role in certain ecosystems long before its atmospheric accumulation.

A revealing multidisciplinary methodology

The team combined genomics, machine learning, and geological data to trace the evolutionary history of bacteria. The analysis of 1,007 modern genomes helped identify transitions toward aerobic metabolism.

The results, published in Science, highlight at least three bacterial lineages that developed this capability before the Great Oxidation. Among them, the ancestor of cyanobacteria, whose photosynthesis later released atmospheric oxygen on a massive scale.

This approach opens new perspectives for studying other evolutionary traits.

Going further: What was the Great Oxidation?

This geochemical upheaval, which occurred approximately 2.4 billion years ago, corresponds to the first sustained accumulation of oxygen in Earth's atmosphere. Before this event, our planet was dominated by reducing environments, where oceanic iron and volcanic gases absorbed any trace of this gas.

The main trigger was the photosynthetic activity of cyanobacteria. These microorganisms produced oxygen as a metabolic byproduct, which first dissolved in the oceans before saturating geochemical reservoirs and escaping into the air. The red bands in iron formations testify to this gradual oxidation.

The consequences were dramatic for the primitive biosphere. Many anaerobic species, unable to tolerate this toxic gas, disappeared, while organisms capable of using it experienced an evolutionary explosion. This pivotal event paved the way for the emergence, billions of years later, of the complex life forms we know today.