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, played a more significant role. First, the Deccan Traps eruptions began about 66 million years ago, well before the asteroid impact, and lasted for nearly a million years. This prolonged volcanic activity would have released vast amounts of sulfur dioxide and carbon dioxide, causing severe climate change—acid rain, global cooling followed by warming—that could have stressed dinosaur populations over time. Second, the fossil record shows a gradual decline in dinosaur diversity in the last few million years of the Cretaceous, not a sudden die-off consistent with an asteroid strike. This decline aligns with the escalating volcanic activity, suggesting a slow environmental deterioration. Third, the Chicxulub crater, often linked to the impact, is dated to exactly the boundary, but volcanic eruptions at the Deccan Traps also exhibit a peak in activity at that same time, meaning the impact may have merely delivered the final blow to already-doomed species. Thus, while the asteroid was a factor, the primary driver of the extinction was likely the Deccan volcanism.
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The reading’s argument that Deccan volcanism was the primary cause of dinosaur extinction is not convincing. First, the timing of the Deccan eruptions does not support a gradual kill mechanism. While eruptions began 66 million years ago, the most intense phase—known as the Poladpur formation—occurred after the asteroid impact, not before. In fact, the majority of lava, about 80%, erupted in a short pulse immediately following the boundary, meaning volcanic climate effects would have been too late to cause the extinction. Second, the claim of a gradual decline in dinosaur fossils is misleading. The apparent decline is likely a sampling artifact: dinosaur fossils are rare in the last few million years because of sea-level regression and poor preservation conditions, not because dinosaurs were already dying out. When corrected for sampling bias, the fossil record shows that dinosaurs were thriving until the very end. Third, the peak in Deccan activity at the boundary is not evidence of a causal role; rather, the impact itself may have triggered increased volcanic activity by causing seismic shaking and crustal fracturing. Thus, the asteroid impact remains the more plausible sole trigger, with volcanism as a secondary consequence, not the primary cause.
📝 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.
