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 prolonged volcanic activity in the Deccan Traps of India was the primary cause. First, the timing of the Deccan eruptions coincides closely with the extinction event. Radiometric dating shows that the main phase of volcanic activity occurred around 66 million years ago, overlapping with the Cretaceous-Paleogene boundary. Second, volcanic emissions would have had severe environmental effects. The Deccan Traps released enormous quantities of sulfur dioxide and carbon dioxide, leading to acid rain, global cooling, and ocean acidification—conditions that could have disrupted ecosystems long before any asteroid strike. Third, the fossil record reveals a gradual decline in dinosaur diversity over the last few hundred thousand years of the Cretaceous, which is more consistent with a slow, ongoing stressor like volcanism rather than a sudden impact. While the asteroid impact may have delivered a final blow, the Deccan volcanism was likely the dominant driver of the mass extinction.
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The lecture challenges the idea that Deccan volcanism was the primary cause of dinosaur extinction, arguing that the asteroid impact was far more decisive. First, although the Deccan eruptions began before the extinction, their most intense phase actually occurred after the Cretaceous-Paleogene boundary. High-precision dating indicates that over 70% of the lava was erupted after the impact, meaning the volcanism could not have been the trigger. Second, the environmental effects of the eruptions were likely less severe than claimed. Recent climate models suggest that the sulfur and carbon dioxide emissions, while significant, were buffered by natural processes over millions of years, and the cooling was not abrupt enough to cause a mass extinction. In contrast, the asteroid impact would have caused an immediate 'impact winter' with a sharp drop in temperature and sunlight, which is more consistent with the sudden collapse seen in the fossil record. Third, the gradual decline in dinosaur fossils may be an artifact of incomplete sampling. When more complete and finely resolved sections are examined, the decline appears to be sudden and coincident with the impact, not a gradual trend. Thus, the lecture concludes that the asteroid, not volcanism, was the primary cause.
📝 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).
