The extinction of the dinosaurs at the end of the Cretaceous period, approximately 66 million years ago, has long fascinated scientists. While the asteroid impact theory is widely accepted, a competing hypothesis suggests that massive volcanic eruptions in the Deccan Traps of India were the primary cause. Proponents of the volcanic theory offer three main arguments. First, the Deccan eruptions occurred over a period of about 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 the asteroid struck. Second, the fossil record shows a gradual decline in dinosaur diversity in the last few million years of the Cretaceous, consistent with a slow environmental deterioration caused by volcanism, rather than a sudden catastrophe. Third, the timing of the Deccan eruptions overlaps with the Cretaceous-Paleogene boundary, and some volcanic ash layers have been dated to the exact time of the mass extinction, suggesting that volcanic activity alone could have driven the extinction without needing an asteroid impact.
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The lecture challenges the volcanic theory, arguing that the asteroid impact was the decisive cause of dinosaur extinction. First, while the Deccan eruptions were prolonged, their climatic effects were not as severe as claimed. Recent climate models show that the volcanic gases caused only moderate warming, not catastrophic cooling, and many species survived through the eruptions. In contrast, the asteroid impact created a sudden global winter, with dust blocking sunlight for months, which would have been far more lethal. Second, the claim of gradual dinosaur decline is misleading. The fossil record is incomplete, and some studies indicate that dinosaur diversity remained high until the very end of the Cretaceous. The apparent decline may be due to sampling biases or regional variations, not a true global trend. Third, the exact timing of the Deccan eruptions is problematic. Most of the volcanic activity occurred about 300,000 years before the mass extinction, and only a small fraction continued past the boundary. In contrast, the Chicxulub impact crater in Mexico is precisely dated to the extinction event, and the impact ejected global debris layers that coincide exactly with the fossil disappearance. Thus, the volcanic eruptions may have weakened ecosystems, but the asteroid impact delivered the final, fatal blow.
📝 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).
