Scientists Just Discovered Bacteria Were Breathing Oxygen A Billion Years Earlier

New research suggests that certain bacteria began using oxygen nearly one billion years earlier than previously thought. The findings could profoundly reshape our understanding of how life evolved on Earth, particularly regarding the origins of respiration and the conditions that made complex life possible.

Early Oxygen Tolerance Long Before The Great Oxidation Event

For decades, scientists believed that bacteria remained strictly anaerobic until the Great Oxidation Event (GOE), approximately 2.4 billion years ago. This milestone marked the first time oxygen began accumulating in the Earth’s atmosphere, dramatically altering the planet’s biosphere.

However, a new study led by Dr. Adrián Arellano Davín of the Okinawa Institute of Science and Technology (OIST) shows that some bacterial lineages adapted to using oxygen as much as 900 million years before the GOE. These findings suggest that oxygen pockets existed in isolated environments well before it became a major atmospheric component.

Genome Analysis Sheds Light On Early Bacterial Respiration

The team employed machine learning and phylogenetic reconciliation across a dataset of 1,007 bacterial genomes to pinpoint where in evolutionary history certain microbes transitioned from anaerobic to aerobic metabolism.

This combined computational and geological approach allowed researchers to build a detailed timeline, estimating when different bacterial groups developed the ability to use oxygen for respiration.

“This combined approach of using genomic data, fossils, and Earth’s geochemical history brings new clarity to evolutionary timelines, especially for microbial groups that don’t have a fossil record,” said Professor Gergely Szöllősi, head of the Model-based Evolutionary Genomics Unit at OIST.

Oxygen-based Metabolism Gave Early Microbes A Survival Edge

Respiring with oxygen is far more efficient than relying on anaerobic processes. Even slight traces of oxygen could have allowed early bacteria to produce more energy, increasing their chances of survival and proliferation.

This advantage may have led aerobic lineages to diversify more rapidly over time, laying the biochemical groundwork for later photosynthetic evolution.

“Our work also shows that modeling microbial traits from their genomes using machine learning works well for studying the spread of aerobic metabolisms,” explained Dr. Tom Williams from the University of Bristol’s School of Biological Sciences.

Linking Oxygen Adaptation To The Rise Of Cyanobacteria

The study also provides new insights into the evolution of cyanobacteria, the microbial group responsible for oxygenic photosynthesis. Evidence suggests that an ancestor of cyanobacteria may have already possessed oxygen tolerance, which could have set the stage for the development of photosynthetic genes.

This supports the idea that oxygen use and photosynthesis may have evolved in parallel rather than in sequence, changing how scientists view the timeline of metabolic innovation in early life.

Microbial History Redefined By Data Fusion

By integrating genomic, fossil, and geochemical evidence, the researchers reconstructed family trees of bacterial evolution stretching back to the Hadean and early Archaean eras, over 3.9 billion years ago. They found that many aerobic traits emerged before the atmospheric shift, though constrained to specific niches.

“This combined use of different data types can help us figure out not only when bacteria evolved but also how they adapted,”  said Dr. Davín.