[2026] PTE Academic Reading - Multiple Choice, Single Answer

The Great Oxygenation Event (GOE), which occurred roughly 2.4 billion years ago, is often celebrated as the catalyst for the evolution of complex, multicellular life. However, this perspective overlooks the fact that for the dominant anaerobic organisms of the time, the sudden influx of oxygen was a catastrophic environmental pollutant. The proliferation of cyanobacteria and their photosynthetic byproducts likely triggered the first and perhaps most significant mass extinction in Earth's history. While the resulting oxidative atmosphere eventually paved the way for aerobic respiration and the rise of the animal kingdom, it did so at the cost of a global biosphere that had thrived for eons. Furthermore, the chemical reaction of oxygen with atmospheric methane likely induced a massive glaciation, turning the planet into a 'snowball' for millions of years. Recognizing the GOE as both a biological revolution and a planetary disaster challenges the anthropocentric narrative that views early Earth's history solely through the lens of human origins. Therefore, the GOE serves as a poignant reminder that progress in one evolutionary branch often necessitates the wholesale destruction of another.