The extinction of the dinosaurs at the end of the Cretaceous period has long been attributed to a massive asteroid impact. However, recent evidence suggests that volcanic activity, specifically the Deccan Traps in India, may have been the primary cause. Three main arguments support this volcanic hypothesis. First, the Deccan Traps eruptions began well before the asteroid impact and lasted for nearly a million years, releasing enormous amounts of sulfur dioxide and carbon dioxide. These gases would have caused severe climate change, including global cooling (volcanic winter) and ocean acidification, which could have stressed ecosystems long before the impact. Second, the fossil record shows a gradual decline in dinosaur diversity and abundance in the last few hundred thousand years of the Cretaceous, consistent with prolonged environmental stress rather than a sudden catastrophic event. Third, the timing of the impact, at Chicxulub in Mexico, coincides with the very end of the Cretaceous, but many marine species disappeared earlier, suggesting that the impact was the final blow to already weakened populations, not the sole cause.
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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 erupted over a long period, recent high-precision dating shows that the most intense phase of volcanic activity occurred after the impact, not before. The early eruptions were relatively mild and may not have released enough gas to cause significant global change. In fact, climate models suggest that the cooling from early eruptions was modest and temporary, unlikely to drive dinosaurs to extinction. Second, the apparent gradual decline in dinosaur fossils may be an artifact of sampling bias. Fossil preservation in the late Cretaceous is poor, and when corrected for rock volume, dinosaur diversity may have remained stable until the impact. Third, the marine extinctions before the impact can be explained by other factors, such as sea-level changes and local anoxia, not necessarily volcanic activity. The impact itself triggered a global catastrophe—fires, tsunamis, and a dust cloud that blocked sunlight—leading to a sudden collapse of food chains. The lecture concludes that the impact was the definitive cause, with volcanic activity playing only a minor role.
📝 Инструкция по письму 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).
