The extinction of the dinosaurs at the end of the Cretaceous period, approximately 66 million years ago, has long fascinated scientists. While the asteroid impact theory is widely accepted, a competing hypothesis proposes that massive volcanic eruptions in the Deccan Traps of India were the primary cause. Proponents of the volcanic theory offer three main arguments. First, the Deccan Traps eruptions were prolonged, lasting for over a million years, and released vast quantities of sulfur dioxide and carbon dioxide. These gases would have caused severe global cooling (via sulfate aerosols) followed by warming (via CO2), creating drastic climate fluctuations that stressed ecosystems long before the asteroid strike. Second, the timing of the eruptions overlaps with the mass extinction, and some geological evidence suggests that the most intense phase of volcanism occurred just before or at the K-Pg boundary, implying a causal link. Third, the volcanic theory explains why some species, such as amphibians and freshwater reptiles, survived while dinosaurs perished: volcanic gases would have affected land and air environments more severely than aquatic habitats, whereas an asteroid impact would have caused a more uniform catastrophe.
🎧 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 hypothesis, arguing that the asteroid impact remains the more plausible cause of dinosaur extinction. First, while volcanic eruptions did release gases, their climatic effects were not as severe or rapid as the lecture suggests. Climate models indicate that the Deccan eruptions caused only moderate, gradual temperature changes over hundreds of thousands of years, giving species time to adapt. In contrast, the asteroid impact triggered a sudden 'impact winter' with a sharp drop in temperature within months, which would have disrupted food chains worldwide. Second, the timing argument is flawed. High-precision radiometric dating shows that the main phase of Deccan volcanism occurred about 250,000 years before the K-Pg boundary, not at the boundary itself. The extinction event coincides exactly with the Chicxulub impact, not with the peak volcanic activity. Third, the survival pattern of species actually supports the impact theory. The lecture notes that freshwater species survived better, but this is consistent with an impact: the impact would have caused widespread fires and tsunamis, but aquatic environments were partially buffered. Moreover, volcanic gases would have produced acid rain, which would have acidified lakes and rivers, harming freshwater life—yet many freshwater species survived. Therefore, the evidence points to the asteroid as the decisive factor.
📝 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.
