TOEFL Integrated Writing

📖 Reading Passage

The extinction of the dinosaurs at the end of the Cretaceous period has long been attributed to a massive asteroid impact. However, a growing body of evidence suggests that volcanic activity, specifically the Deccan Traps in India, was the primary driver of this mass extinction. First, the timing of the Deccan Traps eruptions aligns closely with the extinction event. Geochemical dating shows that the main phase of volcanic activity occurred around 66 million years ago, precisely when the dinosaurs disappeared. Second, volcanic eruptions release vast amounts of sulfur dioxide and carbon dioxide, leading to severe climate changes. Sulfur aerosols cause rapid global cooling, while carbon dioxide induces long-term warming, creating a 'double whammy' that would stress ecosystems. Third, the fossil record indicates a gradual decline in dinosaur diversity in the 500,000 years before the impact, suggesting that volcanic stress had already weakened populations, making them vulnerable to any additional shocks.

🎧 Listening Lecture

The reading's argument for volcanic activity as the main cause of dinosaur extinction is flawed. First, the precise timing of the Deccan Traps' main phase is not as clear-cut. While some eruptions occurred near the extinction boundary, the majority of the lava flows—over 80%—erupted after the extinction, not before. Thus, the volcanic activity could not have caused the extinction; rather, it may have been a consequence of the impact-induced seismic activity. Second, the climate effects of the Deccan Traps were not as severe as the reading claims. Evidence from paleoclimate proxies shows that the temperature changes during the Deccan eruptions were modest and gradual, occurring over hundreds of thousands of years, allowing species to adapt. In contrast, the asteroid impact would have caused an immediate 'impact winter'—a sharp drop in sunlight and temperature lasting years—which is far more devastating. Third, the claimed gradual decline in dinosaur diversity is not supported by high-resolution fossil data. Recent studies using detailed stratigraphic sampling show that dinosaur populations were stable and diverse right up to the last 100,000 years before the impact, with no evidence of a prolonged decline. The apparent decline in some older records is an artifact of incomplete fossil preservation. Therefore, the asteroid impact remains the most plausible cause.