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 extensive volcanic activity, specifically the Deccan Traps eruptions in India, was the primary cause. First, volcanic eruptions released enormous quantities of sulfur dioxide and carbon dioxide, leading to rapid climate change. Sulfur aerosols caused global cooling, while CO2 contributed to long-term warming, creating stress that dinosaurs could not survive. Second, the timing of the Deccan Traps eruptions aligns closely with the extinction event, with the most intense phase occurring just before the boundary layer. This temporal correlation suggests a causal link. Third, the fossil record shows a gradual decline in dinosaur diversity in the millions of years before the impact, consistent with the slow but relentless environmental degradation caused by volcanism, not a sudden catastrophe. Therefore, while an asteroid may have delivered the final blow, volcanic activity was the primary driver of dinosaur extinction.
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The reading argues that volcanic activity was the main cause of dinosaur extinction, but this view is flawed. First, the climate effects of the Deccan Traps were not as severe as claimed. Recent models indicate that volcanic sulfur aerosols may have caused only brief, intermittent cooling, not a prolonged global winter, and the CO2 released was insufficient to cause catastrophic warming. In contrast, an asteroid impact would have thrown dust and soot into the atmosphere, blocking sunlight for months and causing a sudden, drastic drop in temperature—a mechanism well-supported by evidence. Second, the timing argument is misleading. While the Deccan eruptions began before the extinction, their most intense phase actually occurred about 200,000 years after the boundary layer, meaning the peak volcanic activity did not coincide with the mass extinction. The asteroid impact, however, is precisely dated to the boundary. Third, the claim of gradual decline is not supported by recent fossil analyses. When corrected for sampling bias, dinosaur diversity remained high until the very end of the Cretaceous, suggesting that they were thriving until the sudden impact. Thus, the asteroid impact, not volcanism, is the more compelling explanation.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
