The extinction of the dinosaurs at the end of the Cretaceous period has long been attributed to a massive asteroid impact. However, a closer examination of the fossil record and geological evidence suggests that volcanic activity, specifically the Deccan Traps in India, was the primary cause. First, the timing of the Deccan Traps eruptions aligns more precisely with the extinction event. Radiometric dating shows that the main phase of volcanic activity occurred over a relatively short period, coinciding with the iridium layer that marks the extinction. Second, volcanic emissions of sulfur dioxide and carbon dioxide would have caused severe climate changes, including rapid global warming and cooling, which could have stressed dinosaur populations long before any asteroid strike. Third, the fossil record indicates a gradual decline in dinosaur diversity over the last few million years of the Cretaceous, consistent with the prolonged environmental stress from volcanism, rather than a sudden catastrophic impact.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
The lecture challenges the volcanic theory presented in the reading. While the Deccan Traps were indeed active, their most intense eruptions occurred about 100,000 years before the extinction, and the final, smaller pulses happened after the iridium layer. Thus, the timing does not support a direct causal link. Moreover, the climate effects of volcanic gases were likely less severe than the reading suggests; models indicate that sulfate aerosols would have caused short-term cooling, but the long-term warming from CO2 may have been moderate, not enough to drive dinosaurs to extinction. Finally, the claim of a gradual decline in dinosaur diversity is based on incomplete fossil sampling. Many regions show diverse dinosaur communities up to the very end of the Cretaceous, and the apparent decline in some areas can be explained by sea-level regression and preservation biases. The sudden and global nature of the extinction, including the simultaneous demise of many other species, aligns more strongly with an asteroid impact, which would have caused a rapid and catastrophic environmental collapse.
📝 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.
