托福综合写作

📖 阅读文章

The extinction of the dinosaurs at the end of the Cretaceous period, approximately 66 million years ago, has long been attributed to a massive asteroid impact. However, a growing body of evidence suggests that volcanic activity, specifically the Deccan Traps in present-day India, was the primary driver. First, the timing of the Deccan Traps eruptions coincides closely with the extinction event. Radiometric dating indicates that the main phase of volcanic activity lasted for about 700,000 years, beginning just before the extinction and continuing for about 500,000 years after, which matches the geological record of the extinction horizon. Second, volcanic emissions of sulfur dioxide and carbon dioxide would have caused severe climate changes, including global cooling and ocean acidification, sufficient to disrupt ecosystems worldwide. Third, the asteroid impact theory fails to explain the selective nature of the extinction: while many terrestrial species, especially large dinosaurs, perished, many aquatic and small terrestrial species survived, which is inconsistent with a sudden, global catastrophe but more compatible with the gradual, prolonged stress of volcanic activity.

🎧 听力讲座

The lecture challenges the volcanic hypothesis presented in the reading. While acknowledging that the Deccan Traps were active at the end of the Cretaceous, the professor argues that the timing is not as precise as claimed. Recent high-resolution dating shows that the most intense phase of volcanic eruptions occurred about 200,000 years before the extinction event, and by the time of the extinction, volcanic activity had significantly declined. Therefore, the volcanic eruptions were not contemporaneous with the mass die-off. Furthermore, the climate effects of the Deccan Traps were likely too weak to cause a global catastrophe. Sulfur aerosols from the eruptions would have caused short-term cooling, but the total volume of sulfur released was much lower than previously estimated, and carbon dioxide levels would have been buffered by ocean absorption, leading to only minor warming. These effects are not consistent with the rapid, severe environmental changes observed at the extinction boundary. Finally, the selective extinction pattern cited by the reading actually supports the asteroid impact. The impact would have produced a global fireball, dust, and tsunamis, but species that could burrow, live in deep water, or tolerate temporary darkness—such as small mammals, crocodiles, and some fish—would have had a better chance of survival. In contrast, large dinosaurs, with their high metabolic demands and exposed habitats, would have perished quickly, which matches the fossil record better than a gradual volcanic scenario.