TOEFL 통합 작문

📖 읽기 지문

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. First, the timing of the Deccan Traps eruptions aligns closely with the extinction event, spanning the last 400,000 years of the Cretaceous and continuing into the early Paleogene. This prolonged volcanic activity would have released vast amounts of sulfur dioxide and carbon dioxide, causing rapid climate fluctuations, acid rain, and global cooling, which could have stressed ecosystems long before any asteroid hit. Second, the fossil record shows a gradual decline in dinosaur diversity and population sizes in the millions of years leading up to the impact, consistent with a slow-burning environmental crisis rather than a sudden catastrophic event. Finally, the asteroid impact theory fails to explain why many species, including crocodiles, birds, and mammals, survived despite the supposed global firestorm and nuclear winter. In contrast, volcanic emissions would have had more selective effects, sparing organisms adapted to fluctuating climates and toxic atmospheres.

🎧 듣기 강의

The lecture challenges the volcanic theory presented in the reading, arguing that the asteroid impact remains the most plausible explanation for the dinosaurs' demise. First, while the Deccan Traps eruptions were indeed long-lasting, their most intense phase occurred about 300,000 years before the extinction horizon, and the climate changes they caused were not severe enough to trigger a mass extinction. In fact, many dinosaur species thrived during the eruptions, only disappearing abruptly at the impact layer, which contains iridium and shocked quartz—material unique to an asteroid strike. Second, the supposed gradual decline in dinosaur diversity is misleading; recent high-resolution fossil studies show that dinosaur populations were stable and diverse right up to the last 100,000 years before the impact. The apparent decline in older records is due to sampling biases and incomplete preservation. Finally, the survival of crocodiles, birds, and mammals does not contradict the impact theory. These groups included small, generalist, and burrowing or aquatic species that could have survived by exploiting sheltered niches, whereas large, specialized dinosaurs were more vulnerable. Moreover, the impact triggered a brief but catastrophic global cooling and darkness, which would have decimated plant life and disrupted food chains—exactly what the fossil record shows.