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, specifically the Deccan Traps eruptions in India, was the primary driver of this mass extinction. Three key arguments support this volcanic hypothesis. First, the Deccan Traps eruptions released enormous quantities of sulfur dioxide and carbon dioxide over a period of roughly 500,000 years, leading to severe global cooling and ocean acidification. This prolonged environmental stress would have disrupted ecosystems long before any asteroid strike. Second, the fossil record shows a gradual decline in dinosaur diversity and abundance in the million years before the impact, consistent with a slow, volcanic-induced deterioration rather than a sudden catastrophic event. Third, recent high-precision dating of volcanic ash layers interbedded with dinosaur fossils indicates that the most intense phase of Deccan volcanism occurred just before and at the same time as the extinction horizon, suggesting a causal link. While the asteroid impact may have delivered a final blow, the volcanic eruptions likely weakened dinosaur populations to the point of collapse.
🎧 听力讲座
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The lecture challenges the volcanic hypothesis presented in the reading, arguing that the asteroid impact remains the most plausible and primary cause of the dinosaurs' extinction. First, although the Deccan Traps emitted vast amounts of gases, the timing does not align with the extinction event. The most intense volcanic phase actually occurred about 200,000 years before the extinction horizon, and by the time the dinosaurs disappeared, volcanic activity had significantly waned. In contrast, the asteroid impact happened precisely at the extinction boundary, delivering an immediate and catastrophic shock. Second, the claim of a gradual dinosaur decline is not supported by recent paleontological data. High-resolution fossil studies from the latest Cretaceous show that dinosaur populations were stable and diverse right up to the impact event, with no evidence of a prolonged decline attributable to volcanism. The apparent decrease in fossils is likely a sampling artifact due to incomplete rock records. Third, the volcanic ash layers cited in the reading are not contemporaneous with the mass extinction; they were deposited either before or after the event. The iridium layer, a signature of asteroid impact, is found globally at the exact extinction level, while no such unique marker exists for the Deccan eruptions. Therefore, the lecture concludes that the asteroid impact was the decisive cause, with volcanism playing a minor, if any, role.
📝 Instrucciones de escritura 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).
