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, volcanic eruptions released vast amounts of sulfur dioxide and carbon dioxide, leading to rapid climate change. Sulfur aerosols caused a temporary cooling, while CO2 caused long-term warming, both of which would have stressed ecosystems over hundreds of thousands of years. Second, the timing of the Deccan eruptions aligns closely with the extinction event, with the main phase of activity occurring just before the boundary layer that marks the extinction. Third, volcanic activity would have produced toxic gases like hydrogen sulfide and mercury, which could have poisoned both marine and terrestrial life, causing gradual decline rather than the sudden die-off expected from an impact. These factors collectively point to volcanism as the more plausible driver of the end-Cretaceous mass extinction.
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The reading’s argument for volcanism as the primary cause of dinosaur extinction is unconvincing. First, while volcanic gases can alter climate, the magnitude and duration of climate change from an asteroid impact are far more severe. The impact vaporized rock, throwing up dust and soot that blocked sunlight for months, causing a sudden and catastrophic collapse of photosynthesis. Volcanic eruptions, though prolonged, would have allowed ecosystems to adapt gradually. Second, the timing argument is flawed. The main pulse of Deccan volcanism occurred about 300,000 years before the extinction layer, and a later, smaller pulse happened after the extinction. In contrast, the Chicxulub impact in Mexico is precisely dated to within 30,000 years of the boundary, making it the more likely trigger. Third, the claim of toxic gas poisoning is speculative. The amounts of mercury and hydrogen sulfide released by volcanoes are not unique, and such gases are often localized. However, the impact’s global effects—tsunamis, wildfires, and an impact winter—would have been lethal across all continents almost simultaneously. Therefore, the impact scenario remains the strongest explanation for the sudden extinction.
📝 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).
