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 intense volcanic activity in the Deccan Traps of India was the primary cause. First, the Deccan eruptions began approximately 66 million years ago, well before the asteroid impact, and lasted for nearly 30,000 years. This prolonged volcanic activity would have released vast amounts of sulfur dioxide and carbon dioxide, leading to severe global cooling followed by warming, which could have disrupted ecosystems long before any impact. Second, the fossil record shows a gradual decline in dinosaur diversity over the last few million years of the Cretaceous, consistent with the slow, cumulative stress of volcanic emissions rather than a sudden catastrophic event. Finally, recent high-precision dating of Deccan lava flows reveals that the most intense phase of eruptions occurred just before the mass extinction, and the associated environmental changes—such as ocean acidification and ozone depletion—were severe enough to cause a collapse in food chains. Thus, while the asteroid may have delivered the final blow, the volcanic activity was the fundamental driver of the extinction.
🎧 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 idea that volcanic activity was the main cause of dinosaur extinction. While the Deccan eruptions were indeed significant, their timeline does not match the fossil evidence as cleanly as the reading suggests. First, the reading claims that volcanism began before the impact, but recent isotope analyses from marine sediments show that the most severe environmental disruption—a sharp spike in iridium and soot—occurred exactly at the impact boundary, not during the volcanic phase. The volcanic emissions were spread out over hundreds of thousands of years, allowing ecosystems to partially adapt, whereas the impact released energy equivalent to billions of atomic bombs in a single instant, causing immediate tsunamis, wildfires, and a dust cloud that blocked photosynthesis for months. Second, the alleged gradual decline in dinosaur diversity is misleading; many paleontologists argue that the apparent decline is an artifact of incomplete fossil sampling. In fact, high-resolution studies from North America show that dinosaur populations were robust and diverse right up to the impact layer. Third, the most intense volcanic phase actually occurred about 200,000 years before the extinction, and the climate changes it caused were not sufficient to push dinosaurs to the brink. Instead, the impact’s unique effects—such as global acid rain and a prolonged impact winter—are more consistent with the sudden and selective extinction pattern observed in the fossil record. Therefore, the asteroid impact, not volcanism, was 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.
