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 released enormous quantities of sulfur dioxide and carbon dioxide over hundreds of thousands of years, leading to rapid climate change—acid rain, global cooling followed by warming—that would have stressed ecosystems long before any asteroid struck. Second, the timing of the eruptions coincides with the extinction horizon; recent high-precision dating shows that the main phase of volcanism began about 250,000 years before the impact and continued for another 500,000 years after, meaning the environmental disruption was sustained and severe. Third, the fossil record reveals a gradual decline in dinosaur diversity and abundance in the 200,000 years preceding the impact, consistent with a slow, volcanically induced deterioration rather than a sudden catastrophic event. These lines of evidence argue that volcanic activity, not the asteroid, was the decisive factor in the dinosaurs' demise.
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The professor challenges the volcanic hypothesis presented in the reading. While volcanic activity was significant, the evidence points to the asteroid impact as the primary killer. First, the climate effects of the Deccan eruptions were not as severe as claimed. Recent models suggest that sulfur aerosols from the eruptions caused only a few degrees of cooling, not a catastrophic drop, and the ecosystem showed resilience during earlier volcanic phases. Second, the timing argument is flawed: the main pulse of extinction occurred within a few thousand years of the impact, whereas the volcanic activity spanned nearly a million years. If volcanoes were the cause, we would expect a gradual extinction over that entire period, but instead the fossil record shows a sudden disappearance at the impact horizon. Third, the alleged gradual decline in dinosaur fossils is an artifact of sampling—the fossil record is incomplete, and the apparent decline can be explained by changes in sedimentation and preservation conditions. In fact, when adjusted for sampling biases, dinosaur populations were stable until the very end. Thus, the asteroid impact remains the most plausible trigger for the mass extinction.
📝 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).
