The extinction of the dinosaurs at the end of the Cretaceous period, about 66 million years ago, has long been attributed to a massive asteroid impact. However, a growing body of evidence suggests that prolonged volcanic activity in the Deccan Traps of India was the primary cause. First, the Deccan eruptions released enormous quantities of sulfur dioxide and carbon dioxide over hundreds of thousands of years, leading to severe global cooling and ocean acidification. This gradual environmental stress would have disrupted food chains and reproductive cycles long before the impact, making dinosaurs vulnerable to extinction. Second, recent dating of Deccan lava flows shows that the most intense phase of eruptions began about 250,000 years before the impact and continued for another 500,000 years, coinciding with a gradual decline in dinosaur diversity observed in the fossil record. This correlation suggests that volcanic activity, not a sudden impact, drove the extinction. Third, the impact theory fails to explain why many species, such as crocodiles and birds, survived despite being exposed to the same immediate effects of the impact. In contrast, the longer-term, climate-altering effects of volcanism would have selectively harmed large terrestrial animals like dinosaurs while sparing smaller, more adaptable species.
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Professor: The reading's argument for volcanic activity as the main cause of dinosaur extinction is not convincing. First, while the Deccan eruptions did release gases, their effects were spread over hundreds of thousands of years. Earth's climate and ecosystems have buffers—oceans and vegetation can absorb carbon dioxide, and sulfur aerosols dissipate relatively quickly. The fossil record shows no significant global cooling or acidification event at the time of the eruptions. In fact, the dinosaurs thrived for millions of years during the volcanic phase, which contradicts the idea that volcanic stress was fatal. Second, the claimed correlation between the most intense volcanic phase and dinosaur decline is misleading. New high-precision dating reveals that the peak eruptions occurred about 200,000 years after the impact, not before. The dinosaur fossil decline actually starts abruptly at the impact layer, which is consistent with a sudden catastrophe, not a slow volcanic process. Third, the survival of crocodiles and birds actually supports the impact theory. Impact events produce deadly heat pulses and tsunamis, but species living in burrows or aquatic environments, like crocodiles, could escape the immediate blast. Birds, being small and able to fly, could find refuge. In contrast, large dinosaurs had no such shelter. So, the pattern of survival aligns perfectly with a sudden impact, not with the prolonged volcanic scenario.
📝 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.
