การเขียนเชิงบูรณาการ TOEFL

📖 เนื้อเรื่อง

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, an alternative hypothesis proposes that massive volcanic eruptions in the Deccan Traps of India were the primary cause. Three main arguments support this volcanic theory. First, the Deccan eruptions lasted for roughly 30,000 years, releasing enormous amounts of sulfur dioxide and carbon dioxide. These gases would have caused severe global cooling and acid rain, stressing ecosystems long before any asteroid struck. Second, the timing of the eruptions overlaps with the extinction event. Recent radiometric dating places the main phase of Deccan volcanism at precisely the Cretaceous-Paleogene boundary, suggesting a causal link. Third, volcanic eruptions produce dramatic short-term climate fluctuations, including rapid warming from CO2 and cooling from sulfate aerosols. Such instability alone could have disrupted food chains and led to mass extinction, even without an asteroid impact.

🎧 การบรรยาย

The lecture challenges the volcanic theory. While the Deccan eruptions were indeed massive, their role in the extinction is overstated. First, the eruptions were not continuous but occurred in pulses, with long quiet periods between phases. During these quiet intervals, ecosystems could have recovered, so the cumulative stress was less severe than implied. Second, improved dating shows that the most intense volcanic activity actually began about 300,000 years before the extinction event and had largely subsided by the time of the boundary. The final extinction coincides precisely with the asteroid impact, not with peak volcanism. Third, climate models indicate that volcanic gases, while significant, could not produce the sudden and extreme temperature drop inferred from the fossil record. In contrast, an asteroid impact would have ejected dust and sulfur into the stratosphere, blocking sunlight for months and causing a rapid, catastrophic collapse of photosynthesis. The lecture concludes that volcanism may have weakened ecosystems, but the asteroid was the decisive blow.