Microbial life reigns supreme on Earth, yet unraveling its complex history is no small feat—fossils are scarce! A new groundbreaking study sheds light on when certain bacteria first started using oxygen, a game-changer for our understanding of life’s evolution.

Published in the prestigious journal Science, this research, spearheaded by the Model-Based Evolutionary Genomics Unit at the Okinawa Institute of Science and Technology (OIST) along with international collaborators, develops a groundbreaking timeline showcasing how bacteria adapted to oxygen long before the phenomenon of widespread photosynthesis took root.

The Great Oxygenation Event—A Turning Point for Life

Around 2.3 billion years ago, the Great Oxygenation Event (GOE) dramatically transformed our planet's atmosphere. This major shift, fueled by cyanobacteria's oxygen-producing photosynthesis, marked the beginning of oxygen becoming a staple in Earth's environment. It has long puzzled scientists how bacteria adapted during this seismic shift.

Historians of life have struggled to pin down accurate timelines for microbial evolution, mainly due to sparse fossil records and the complexities of determining the ages of ancient bacteria. The only reliable chronological marker dates back to the planet’s formation around 4.5 billion years ago when cosmic impacts likely wiped out early life forms.

Innovative Methodology for Uncovering the Past

Now, an innovative approach combining geological findings with genomic analysis has opened new doors. The researchers ingeniously used the GOE as a benchmark, suggesting that most aerobic bacteria branches would be dated no earlier than this pivotal moment—unless stronger evidence contradicted this.

Using Bayesian statistics, they crafted a model that flexibly accommodates data deviations, determining which ancient lineages likely thrived on oxygen. By simulating probabilities about ancient genomes and employing machine-learning techniques, they could predict oxygen usage in these early life forms.

Astonishing Discoveries About Early Aerobic Bacteria

Their findings revealed that at least three distinct bacterial lineages were utilizing oxygen as far back as 900 million years prior to the GOE, indicating that aerobic processes likely developed well before oxygen flooded the atmosphere. This suggests that the capacity for oxygen utilization may have laid the groundwork for the evolution of oxygenic photosynthesis itself!

Moreover, research estimates that the last common ancestor of all modern bacteria existed between 4.4 and 3.9 billion years ago. The roots of many prominent bacterial groups trace back to the Archaean and Proterozoic eras, coinciding with the emergence of multicellular life.

The Oxygen Connection: A Catalyst for Evolution

As atmospheric oxygen rose during the GOE, aerobic bacteria diversified at a rapid pace compared to their anaerobic cousins, showcasing the dynamic interplay between oxygen levels and microbial evolution. This study illuminates how the availability of oxygen played a crucial role in shaping the biodiversity we witness today.

Prof. Gergely Szöllősi, leading the research team, emphasized the clarity gained through combining genomic data with fossil and geochemical history, especially for those microbial groups lacking fossil records. Dr. Tom Williams from the University of Bristol added that utilizing machine learning for modeling microbial traits may unlock further understanding of how life has evolved alongside Earth’s ever-changing environment.