托福综合写作

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The extinction of the dinosaurs at the end of the Cretaceous period, approximately 66 million years ago, has long been a subject of scientific debate. While the asteroid impact theory is widely accepted, a growing body of evidence suggests that massive volcanic eruptions in the Deccan Traps of India were the primary cause. First, the Deccan eruptions released enormous quantities of sulfur dioxide and carbon dioxide over a period of hundreds of thousands of years, leading to severe global cooling followed by prolonged warming. Such drastic climate shifts would have disrupted food chains and habitats, stressing dinosaur populations long before the asteroid struck. Second, fossil records indicate a gradual decline in dinosaur diversity during the last few million years of the Cretaceous, consistent with a slow, volcanic-driven environmental deterioration rather than a sudden catastrophic event. Third, the timing of the Deccan volcanism aligns closely with the extinction horizon; recent radiometric dating places the main phase of eruptions precisely at the Cretaceous-Paleogene boundary. Therefore, while an asteroid may have delivered a final blow, the Deccan eruptions were the decisive factor in the dinosaurs' demise.

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The reading presents a compelling case for volcanic activity as the primary cause of dinosaur extinction, but the argument fails under scrutiny. First, although the Deccan eruptions were massive, their climatic effects were likely not severe enough to cause global extinction. Climate models show that the sulfur dioxide aerosols would have caused a temporary cooling of only a few degrees, and the subsequent warming was gradual, giving ecosystems time to adapt. In contrast, an asteroid impact would have ejected dust and soot into the stratosphere, blocking sunlight for months and causing a sudden, catastrophic drop in temperature—a scenario far more lethal. Second, the supposed gradual decline in dinosaur diversity is misleading. The fossil record is incomplete, and the apparent decline may reflect sampling biases, not actual population trends. Many studies show that dinosaurs were thriving until the very end of the Cretaceous. Third, the timing argument is flawed: while the Deccan volcanism peaked near the boundary, the eruptions began hundreds of thousands of years before and continued after the extinction, meaning they were not a singular event. In fact, the most intense phase of eruptions occurred after the impact, not before. Thus, the asteroid impact remains the most plausible and rapid cause of the mass extinction.