The extinction of the dinosaurs at the end of the Cretaceous period, about 66 million years ago, is one of the most debated events in Earth's history. While many scientists support the asteroid impact theory, a closer examination of the evidence suggests that massive volcanic eruptions, specifically the Deccan Traps in India, were the primary cause. First, the timing of the Deccan Traps eruptions aligns more precisely with the extinction event. The eruptions began well before the asteroid impact and continued for hundreds of thousands of years after, with the most intense phase coinciding with the extinction horizon. This prolonged volcanic activity would have released enormous amounts of sulfur dioxide and carbon dioxide, causing severe global cooling and ocean acidification, which could have disrupted ecosystems over a long period. Second, the fossil record shows a gradual decline in dinosaur diversity millions of years before the impact, indicating that dinosaurs were already stressed by environmental changes, likely due to volcanic emissions. Third, the asteroid impact, while catastrophic locally, may not have caused a global mass extinction; for example, many species that were sensitive to environmental changes survived the impact, suggesting that the impact's effects were not universally lethal. In contrast, the Deccan Traps' continuous greenhouse gas emissions would have created a cumulative stress that pushed many species over the edge, leading to a more gradual but ultimately devastating extinction.
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The reading's argument that volcanic eruptions were the primary cause of dinosaur extinction is not convincing. First, the timing argument is flawed. While the Deccan Traps were active over a long period, the most intense phase of eruptions occurred about 200,000 years before the impact, and the extinction event itself is precisely dated to the impact layer, which contains iridium and shocked quartz. If volcanoes were the main cause, we would expect a gradual extinction pattern across the eruption period, but the fossil record shows a sudden extinction around the impact, not a gradual decline. Second, the claim of a pre-impact decline in dinosaur diversity is based on incomplete data. Recent studies using more robust statistical methods, that correct for sampling bias, show that dinosaur diversity was actually stable until the very end of the Cretaceous. The apparent decline in older studies is an artifact of incomplete fossil preservation. Third, the argument that many species survived the impact ignores the fact that the impact caused a global catastrophe, including wildfires, tsunamis, and a dust cloud that blocked sunlight for months, leading to a collapse of photosynthesis. Species that survived were those that could endure long periods of darkness and food shortages, such as small mammals and some birds. Furthermore, the impact is linked to the extinction of about 75% of all species, including ammonites and many marine reptiles, which were not particularly sensitive to volcanic gases. This global pattern is more consistent with a sudden, catastrophic event than with gradual volcanic stress.
📝 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).
