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, played a more significant role. First, the timing of the Deccan Traps eruptions aligns closely with the extinction event. Radiometric dating shows that the main phase of volcanic activity occurred about 66 million years ago, precisely when the dinosaurs disappeared, whereas the Chicxulub impact occurred roughly 300,000 years earlier, making it less temporally correlated. Second, volcanic emissions of sulfur dioxide and carbon dioxide would have caused severe climate change, including global cooling and ocean acidification, over tens of thousands of years. Such prolonged environmental stress would have disrupted food chains and habitats, leading to a gradual decline in dinosaur populations long before any impact. Fossil records indicate a decline in dinosaur diversity in the last few million years of the Cretaceous, consistent with volcanic-induced stress. Third, the Deccan Traps eruptions released vast amounts of toxic gases, including mercury and fluorine, which would have poisoned ecosystems. Sedimentary layers from the period show elevated mercury levels, suggesting widespread environmental toxicity that could have directly caused extinction.
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The lecture challenges the volcanic hypothesis presented in the reading. First, while the timing of the Deccan Traps is close to the extinction, the Chicxulub impact is now dated to within 30,000 years of the boundary, making it a more precise and immediate cause. The reading’s claim of a 300,000-year gap is outdated; recent high-precision dating places the impact at the exact extinction horizon. Second, the gradual decline in dinosaur diversity cited in the reading is misleading. Studies of dinosaur fossils show that they were thriving until the very end, with no evidence of a long-term decline. Any apparent decline is likely due to sampling biases or regional variations, not volcanic stress. Third, mercury anomalies are not unique to volcanism; the impact itself could have released mercury from target rocks. Moreover, the toxic effects of volcanic gases would have been localized and not globally lethal. In contrast, the impact caused a sudden, catastrophic event—global wildfires, tsunamis, and a dust cloud that blocked sunlight for months—leading to a rapid mass extinction, which is more consistent with the fossil record showing abrupt disappearance of species.
📝 คำแนะนำการเขียน 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).
