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 cause. First, the timing of the Deccan Traps eruptions coincides with the extinction event. Geochemical dating shows that the main phase of volcanic activity occurred around 66 million years ago, exactly when the dinosaurs disappeared. Second, volcanic eruptions would have released vast amounts of sulfur dioxide and carbon dioxide, leading to severe climate changes, including global cooling and acid rain, which could have disrupted ecosystems worldwide. Third, the fossil record indicates a gradual decline in dinosaur diversity before the impact, suggesting that environmental stress from volcanism had already weakened dinosaur populations, making them vulnerable to any further perturbation.
🎧 听力讲座
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The lecture challenges the volcanic theory presented in the reading. While the timing of the Deccan Traps is indeed close to the extinction, the lecture points out that the most intense volcanic phase occurred about 300,000 years before the extinction, and the eruptions continued for millions of years without causing immediate mass extinction. This suggests that volcanism alone was not sufficient. Furthermore, the climate effects of volcanism, though significant, were likely not as extreme as proposed; models show that volcanic aerosols would have caused a short-term cooling, but the long-term warming from carbon dioxide would have been gradual, not catastrophic enough to kill off dinosaurs. Finally, the claim of a gradual decline in dinosaur diversity is disputed; recent high-resolution fossil studies show that dinosaur populations were thriving right up to the last few thousand years before the extinction, with no evidence of prolonged decline. Instead, the sudden and selective extinction pattern—where large terrestrial animals perished while many small species survived—is more consistent with a sudden impact event that caused a brief but severe global catastrophe, such as darkness and cooling from impact dust.
📝 ライティング指示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
