การเขียนเชิงบูรณาการ TOEFL

📖 เนื้อเรื่อง

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 eruptions in India, was the primary driver. First, the timing of the Deccan Traps eruptions overlaps with the extinction event. Radiometric dating shows that the main phase of volcanic activity occurred around 66 million years ago, precisely when the dinosaurs disappeared. This coincidence suggests a causal link. Second, volcanic eruptions released enormous quantities of sulfur dioxide and carbon dioxide, leading to severe climate change. Sulfur aerosols caused rapid global cooling, while carbon dioxide caused long-term warming, creating a 'push-pull' effect that destabilized ecosystems. Third, the fossil record reveals a gradual decline in dinosaur diversity in the 500,000 years before the impact, which is more consistent with a slow, persistent stressor like volcanism than with a sudden catastrophic impact. Therefore, the Deccan Traps, not the asteroid, were the main cause of the end-Cretaceous extinction.

🎧 การบรรยาย

The reading's argument for volcanic activity as the main cause of dinosaur extinction is flawed. First, the timing argument is misleading. Although the Deccan Traps began erupting before the extinction, the most intense phase of eruptions occurred about 200,000 years after the extinction event. The early eruptions were relatively mild and unlikely to cause global devastation. In contrast, the Chicxulub impact occurred exactly at the extinction boundary, within a narrow window of 30,000 years. Second, the climate effects of volcanism were not as severe as claimed. Studies of sediment cores from the period show that temperature fluctuations during the Deccan eruptions were modest and within the range that many species could tolerate. The impact, however, generated a global dust cloud that blocked sunlight for months, causing a sudden and catastrophic collapse of photosynthesis. Third, the fossil record does not support a gradual decline. Recent high-resolution studies of dinosaur fossils in North America show that dinosaurs were thriving until the very end. The apparent decline in diversity is an artifact of sampling bias, as fewer fossil-bearing sediments exist from the latest Cretaceous. Thus, the abrupt extinction pattern points to a sudden, external event—the asteroid impact—not prolonged volcanic activity.