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, as radiometric dating shows that the main phase of volcanic activity occurred just before and at the boundary layer. Second, volcanic emissions of sulfur dioxide and carbon dioxide would have caused severe climate change, including rapid cooling and ocean acidification, which matches the patterns of selective extinction seen in the fossil record—marine organisms with calcium carbonate shells were particularly hard hit. Third, the asteroid impact theory fails to explain why many species, such as dinosaurs, went extinct globally while other groups like crocodiles and turtles survived; volcanic stress would have been more gradual, allowing less hardy species to die out first, but the impact would have caused a sudden, uniform catastrophe that cannot account for these survival patterns.
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The professor argues that the volcanic hypothesis is flawed and that the asteroid impact remains the most plausible explanation. First, while the Deccan eruptions began before the extinction, their most intense phase actually occurred about 300,000 years after the boundary layer, meaning the worst volcanic activity did not coincide with the mass die-off. In contrast, the Chicxulub impact in Mexico is precisely dated to the extinction boundary, within a margin of only 30,000 years. Second, the climate effects of the Deccan eruptions were likely not severe enough to cause global extinction; volcanic sulfur aerosols would have caused short-term cooling, but the geological record shows that temperatures fluctuated moderately, not catastrophically, and many ocean species survived despite acidification. In fact, the selective extinction pattern can be better explained by the impact: the impact would have caused a brief but intense global winter and a shutdown of photosynthesis, hitting large terrestrial animals like dinosaurs hard, while smaller, burrowing, or aquatic species could have weathered the crisis. Third, the survival of crocodiles and turtles is not evidence against the impact, because these animals are ectothermic (cold-blooded) and have lower metabolic rates, enabling them to survive long periods without food, whereas dinosaurs were endothermic and required large amounts of energy, making them far more vulnerable to a sudden collapse in food chains. Thus, the impact theory is fully consistent with the survival patterns.
📝 Инструкция по письму 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).
