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 driver of this mass extinction. Three main arguments support this volcanic hypothesis. First, the Deccan Traps eruptions, which lasted for approximately 30,000 years, released enormous quantities of sulfur dioxide and carbon dioxide into the atmosphere, causing severe global cooling and ocean acidification that would have stressed ecosystems long before any asteroid struck. Second, the timing of the extinction, dated at 66 million years ago, coincides with the peak of the Deccan eruptions, whereas the Chicxulub impact occurred about 300,000 years earlier, making it less temporally aligned with the extinction event. Third, fossil and sediment records from the late Cretaceous show a gradual decline in dinosaur diversity and marine species over the last few hundred thousand years, consistent with the prolonged environmental stress from volcanism, rather than a sudden catastrophe. Thus, the Deccan volcanism, not the asteroid, was the decisive factor.
🎧 听力讲座
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The lecture challenges the volcanic hypothesis presented in the reading. While the Deccan eruptions were indeed massive, their role in the extinction is overstated. First, although the eruptions lasted 30,000 years, their environmental impact was not continuous; recent geochemical analyses show that the most intense sulfur emissions occurred in brief pulses, separated by long quiescent periods, allowing ecosystems to recover between pulses. The truly catastrophic conditions only occurred after the Chicxulub impact. Second, the reading's timing argument is flawed. High-precision radiometric dating now places the Chicxulub impact at exactly 66 million years ago, matching the extinction layer, while the main phase of Deccan volcanism ended about 200,000 years before the boundary. The earlier eruptions may have weakened ecosystems, but they did not cause extinction. Third, the gradual decline in species diversity observed in the fossil record can be explained by the impact's secondary effects, such as global wildfires and a nuclear winter that disrupted food chains over several years, which would leave a gradual-looking pattern in coarse sediment records. The impact also triggered a second, smaller pulse of Deccan volcanism, confusing the cause-and-effect relationship. Therefore, the asteroid remains the primary trigger.
📝 작문 지시 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
