The extinction of the dinosaurs at the end of the Cretaceous period has long been attributed to a massive asteroid impact. However, a more nuanced view suggests that volcanic activity, specifically the Deccan Traps eruptions in India, was the primary driver. Three key arguments support this volcanic hypothesis. First, the Deccan Traps eruptions lasted for over a million years, releasing enormous amounts of sulfur dioxide and carbon dioxide, which would have caused severe climate change, including global cooling and ocean acidification, well before the asteroid impact. Second, the fossil record shows a gradual decline in dinosaur diversity over the last few million years of the Cretaceous, consistent with prolonged volcanic stress rather than a sudden catastrophe. Third, recent high-precision dating indicates that the main phase of Deccan volcanism began slightly before the asteroid impact, and the impact itself may have triggered even more intense eruptions, meaning the volcanoes were already destabilizing ecosystems before the asteroid struck.
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The lecture challenges the volcanic hypothesis presented in the reading. While the Deccan Traps were indeed massive, their climatic effects were likely not severe enough to cause extinction. For instance, sulfur dioxide aerosols might cause short-term cooling, but the eruptions also released vast amounts of carbon dioxide, a greenhouse gas, which would have offset cooling and led to long-term warming. This warming, however, was gradual and within the tolerance range of most dinosaurs. Second, the claim of a gradual decline in dinosaur diversity is based on incomplete fossil records; many regions show no decline until the very end of the Cretaceous, and the apparent decline may be a sampling artifact. Third, although volcanism began before the impact, the most intense eruptions occurred after the impact, and the extinction event itself is precisely dated to the impact layer, with over 75% of species vanishing within a short geological instant. The lecture concludes that the asteroid impact remains the most plausible cause, as the volcanic activity alone cannot explain the sudden and selective nature of the extinction.
📝 Writing Prompt 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).
