TOEFL 통합 작문

📖 읽기 지문

The extinction of the dinosaurs at the end of the Cretaceous period, about 66 million years ago, has long fascinated scientists. While the asteroid impact theory is widely accepted, a lesser-known hypothesis proposes that massive volcanic eruptions in the Deccan Traps of India were the primary cause. This volcanic theory rests on three main arguments. First, the Deccan Traps eruptions were prolonged, lasting for roughly 30,000 years, and released enormous quantities of sulfur dioxide and carbon dioxide. These gases would have caused severe acid rain and a rapid greenhouse effect, leading to drastic climate swings that could have stressed ecosystems over a long period, well before the asteroid impact. Second, recent high-precision dating suggests that the most intense phase of Deccan volcanism occurred just before the mass extinction event, within a few hundred thousand years, making the timing more consistent with a volcanic cause than an instantaneous impact. Third, the fossil record shows a gradual decline in dinosaur diversity in the million years before the extinction, which aligns with a slow, ongoing environmental stress, not a sudden catastrophic event. Proponents argue that these lines of evidence collectively indicate that volcanism, not an asteroid, was the decisive factor in the dinosaurs' demise.

🎧 듣기 강의

The lecture challenges the volcanic theory presented in the reading. While the Deccan Traps eruptions were indeed massive, their duration and intensity do not support them as the primary cause. First, the reading claims prolonged volcanic activity caused gradual climate stress, but the most severe environmental effects, such as sulfur aerosol-induced cooling, would have been short-lived and localized. Climate models show that the cooling from volcanic aerosols would have been temporary, not sustained over thousands of years, whereas the asteroid impact caused a global 'impact winter' with debris blocking sunlight for months or years—a much more lethal scenario for large animals. Second, although high-precision dating places intense volcanism near the extinction, this coincidence does not prove causation. In fact, the asteroid impact at Chicxulub occurred precisely at the boundary layer, and the impact itself could have triggered enhanced volcanic activity, making volcanism a consequence, not a cause. Third, the reading's claim of gradual dinosaur decline is based on incomplete fossil data. More recent studies in North America show that dinosaur diversity was stable and high until the very end of the Cretaceous, with no evidence of a prolonged decline. The apparent decline in some regions may reflect sampling biases rather than true ecological stress. Thus, the lecture argues that the asteroid impact remains the more plausible primary cause, with volcanism playing a secondary role at best.