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. Radiometric dating shows that the main phase of volcanic activity occurred over a relatively short period, roughly 66 million years ago, which is exactly when the dinosaurs disappeared. This temporal correlation is too precise to be coincidental, suggesting a causal link. Second, volcanic eruptions release vast amounts of sulfur dioxide and carbon dioxide, which can cause severe climate change. Sulfur aerosols reflect sunlight, causing a global cooling or 'volcanic winter,' while carbon dioxide traps heat, leading to long-term warming. Such drastic temperature fluctuations would have stressed ecosystems and disrupted food chains, ultimately leading to mass extinction. Third, the fossil record indicates a gradual decline in dinosaur diversity in the millions of years before the impact, which is more consistent with a prolonged volcanic stress rather than a sudden asteroid strike. The Deccan Traps would have emitted toxic gases and particulates over hundreds of thousands of years, gradually degrading habitats and pushing many species to extinction before the final blow.
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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 most precise dating shows that the main pulse of eruptions occurred about 300,000 years before the extinction event, and a second, smaller pulse occurred after. This gap undermines the idea that volcanic activity directly caused the extinction. Moreover, the climate effects of volcanic gases are not as severe as proposed. The sulfur dioxide from the Deccan Traps would have caused cooling, but geological evidence from deep-sea sediments indicates that the temperature change was modest—only about 2 to 3 degrees Celsius—not enough to trigger a global mass extinction. In fact, many species, including crocodiles and mammals, survived these fluctuations, suggesting that the climate stress was not extreme. Finally, the claim of a gradual decline in dinosaur diversity is not supported by recent fossil studies. High-resolution analyses of dinosaur fossils in North America show that dinosaur populations were stable and diverse right up to the last 100,000 years before the extinction. The apparent decline in some locations is due to sampling biases, such as incomplete fossil preservation. In contrast, the asteroid impact at Chicxulub would have caused immediate catastrophic effects, including a global fireball, tsunamis, and a dust cloud blocking sunlight for months, which better explains the sudden and selective extinction of dinosaurs.
📝 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).
