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 present-day India, was the primary driver. First, the timing of the eruptions aligns closely with the extinction event. Geochemical dating indicates that the Deccan Traps began erupting about 66 million years ago, just before the mass extinction, and continued for roughly 30,000 years. This temporal overlap is too precise to be coincidental. Second, volcanic emissions would have caused severe environmental stress. The eruptions released enormous quantities of sulfur dioxide and carbon dioxide, leading to acid rain, global cooling followed by long-term warming, and ocean acidification. Such rapid climate shifts would have disrupted food chains and habitats, making it difficult for many species, including dinosaurs, to survive. Third, the fossil record shows a gradual decline in dinosaur diversity in the million years before the impact. This pattern suggests that dinosaurs were already struggling due to volcanic-induced environmental changes, and the asteroid impact only delivered the final blow. In contrast, the asteroid impact, while catastrophic locally, produced short-term effects such as dust and fires, but these were unlikely to cause a global extinction lasting thousands of years.
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The lecture challenges the volcanic hypothesis, arguing that the asteroid impact remains the most plausible explanation. First, while the Deccan Traps eruptions did coincide with the extinction, the most intense phase of volcanic activity actually occurred about 300,000 years before the extinction event. The timing is therefore not as precise as the reading suggests; the peak of volcanic emissions happened well before the dinosaurs disappeared, and by the time of the extinction, volcanic activity had decreased significantly. Second, the environmental effects of volcanic emissions were likely not severe enough to cause mass extinction. Sulfur aerosols might have caused temporary cooling, but the overall temperature change was modest, and many species, including crocodiles and mammals, survived despite being sensitive to climate change. Moreover, ocean acidification from volcanic CO2 would have been gradual, allowing marine organisms to adapt, whereas the asteroid impact caused a sudden, dramatic acidification. Third, the fossil record does not support a gradual decline. Recent high-resolution studies in North America show that dinosaur diversity was stable until the very end of the Cretaceous, with no evidence of a long-term decline. Instead, the sudden disappearance of dinosaurs coincides exactly with the iridium layer, a signature of the asteroid impact. Thus, the volcanic hypothesis fails to explain the abrupt nature of the extinction, which is better accounted for by the impact's immediate and catastrophic effects.
📝 Hướng dẫn viết 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).
