The extinction of the dinosaurs at the end of the Cretaceous period, about 66 million years ago, has long been attributed to a massive asteroid impact. However, a growing body of evidence suggests that massive volcanic eruptions in the Deccan Traps of India were the primary cause. First, the Deccan eruptions occurred over a period of roughly 1 million years, releasing enormous amounts of sulfur dioxide and carbon dioxide. These gases would have caused severe global cooling and ocean acidification, creating long-term environmental stress that gradually destabilized ecosystems. Second, the fossil record shows a gradual decline in dinosaur diversity in the 2 million years before the impact, consistent with a slow, volcanic-driven deterioration rather than a sudden catastrophe. Third, recent geochronological dating has revealed that the main phase of Deccan volcanism began about 250,000 years before the Chicxulub impact, meaning that volcanic effects were already underway when the asteroid struck. Thus, while the impact may have delivered a final blow, the Deccan eruptions were the decisive factor in the dinosaurs' demise.
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The lecture challenges the idea that Deccan volcanism was the primary cause of dinosaur extinction. First, while volcanic gases can cause cooling, the Deccan eruptions also released vast amounts of carbon dioxide, a greenhouse gas, leading to long-term warming after initial cooling. However, the extinction event itself was geologically instantaneous, not a gradual decline over hundreds of millennia. In fact, detailed stratigraphic studies show that dinosaur fossils disappear abruptly at the Cretaceous-Paleogene boundary, with no evidence of a prolonged decline. Second, the apparent decline in dinosaur diversity before the impact may be a sampling artifact. The fossil record from the Late Cretaceous is incomplete, and recent finds in North America indicate that dinosaur populations were thriving right up to the impact. Third, the timing of volcanism does not support its role as the killer. The most intense phase of Deccan eruptions occurred about 300,000 years after the impact, not before. The earlier volcanic activity was relatively mild and did not coincide with the mass extinction. Therefore, the abruptness and timing of the extinction point squarely to the asteroid impact as the primary cause, not the volcanic eruptions.
📝 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).
