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 intense volcanic activity, specifically the Deccan Traps eruptions in India, was the primary cause. First, the timing of the eruptions aligns closely with the extinction event. Radiometric dating shows that the main phase of Deccan volcanism occurred around 66 million years ago, spanning the same period as the dinosaur extinction. Second, volcanic emissions would have caused severe environmental stress. The Deccan Traps released enormous quantities of sulfur dioxide and carbon dioxide, leading to acid rain, global cooling followed by warming, and ocean acidification—conditions that could have disrupted ecosystems long before any impact. Third, the fossil record shows a gradual decline in dinosaur diversity in the millions of years before the asteroid impact, suggesting that volcanic activity had already weakened dinosaur populations, making them vulnerable to eventual collapse. Thus, while the asteroid may have delivered the final blow, the Deccan Traps volcanism was the decisive factor in the dinosaurs' demise.

🎧 Listening Lecture

The argument that Deccan volcanism was the primary cause of dinosaur extinction is not convincing. First, although the Deccan eruptions began around 66 million years ago, their most intense phase actually occurred about 300,000 years before the extinction event, not at the same time. The extinction horizon, marked by iridium and shocked quartz, coincides precisely with the Chicxulub impact, not with the peak volcanic activity. Second, while volcanic gases can cause climate change, the severity and duration of the environmental effects from the Deccan Traps were likely insufficient to cause a global mass extinction. Climate models indicate that volcanic emissions produced gradual fluctuations, whereas the impact would have caused a sudden 'impact winter' with a sharp drop in temperature and sunlight, which is more consistent with the rapid extinction observed in the fossil record. Third, the claim of a gradual decline in dinosaur diversity is based on incomplete fossil sampling. Recent studies using improved dating and statistical methods show that dinosaur populations were stable and diverse until the very end of the Cretaceous. The apparent decline is an artifact of the fossil record, not a real biological trend. Therefore, the asteroid impact remains the most plausible cause of the extinction.