Scientists from the University of Queensland, along with international collaborators, have constructed a detailed timeline of bacterial evolution. This groundbreaking research suggests that some bacteria utilized oxygen long before they evolved the ability to produce it through photosynthesis. This discovery, published recently, reshapes our understanding of early life on Earth.
The research team focused on how microorganisms responded to the Great Oxygenation Event (GOE) approximately 2.33 billion years ago. This event dramatically altered Earth's atmosphere, transforming it from one largely devoid of oxygen to one that supports life as we know it. Professor Phil Hugenholtz from UQ highlighted the challenges in establishing accurate timelines due to the scarcity of fossil evidence.
The team overcame these challenges by analyzing geological and genomic records concurrently. They used the GOE as a critical time boundary, assuming that most aerobic bacteria lineages are unlikely to predate this event unless other evidence suggested otherwise. Machine learning was employed to predict whether ancestral bacteria used oxygen. This approach allowed researchers to estimate when specific events occurred, including the emergence of aerobic metabolism.
The findings reveal that at least three aerobic lineages existed before the GOE, by nearly 900 million years. This indicates that the capacity to use oxygen evolved well before its widespread presence in the atmosphere. Evidence suggests the earliest aerobic transition occurred around 3.2 billion years ago in the cyanobacterial ancestor. This discovery opens the door to understanding how bacteria might be resistant to antibiotics.