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 timing of the Deccan eruptions aligns closely with the extinction event. Radiometric dating places the main phase of volcanic activity at approximately 66 million years ago, coinciding with the Cretaceous-Paleogene boundary. Second, volcanic gases, particularly sulfur dioxide and carbon dioxide, would have caused severe climate change. Sulfur aerosols could have blocked sunlight, leading to a global volcanic winter, while CO2 emissions would have caused long-term warming, disrupting ecosystems. Third, the fossil record shows a gradual decline in dinosaur diversity in the million years before the impact, which is more consistent with the prolonged stress of volcanic activity than with a sudden asteroid strike. These factors collectively indicate that volcanism, not an impact, was the decisive driver of the end-Cretaceous mass extinction.
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The lecture challenges the volcanic hypothesis, arguing that the asteroid impact remains the most compelling explanation. First, although the Deccan eruptions began around 66 million years ago, their most intense phase actually occurred about 300,000 years before the extinction event, and the eruptions continued after it. This timing mismatch undermines the claim that volcanism coincided with the mass die-off. Second, the climate effects of volcanic gases were likely less severe than proposed. Recent climate models suggest that sulfur aerosols from the Deccan eruptions were largely offset by simultaneous warming from CO2, resulting in relatively moderate temperature fluctuations that many species could tolerate. In contrast, the asteroid impact would have injected dust and soot into the stratosphere, causing a sudden and catastrophic drop in sunlight and photosynthesis. Third, the fossil record does not show a simple gradual decline; instead, it reveals that dinosaur diversity was stable until the very end of the Cretaceous, with a rapid disappearance at the boundary. This pattern is more consistent with a sudden, catastrophic event like an asteroid impact, not a slow volcanic buildup. Therefore, the lecture concludes that the impact hypothesis remains robust.
📝 Writing Prompt 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).
