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 volcanic activity, specifically the Deccan Traps eruptions in present-day India, was the primary cause. First, the timing of the Deccan Traps eruptions coincides with the extinction event. Geochemical dating shows that the main phase of volcanic activity occurred around 66 million years ago, precisely when the dinosaurs disappeared. Second, volcanic eruptions release vast amounts of sulfur dioxide and carbon dioxide, which can cause severe climate change. Sulfur aerosols block sunlight, leading to a global cooling, while carbon dioxide contributes to long-term warming. Such rapid temperature fluctuations would have stressed ecosystems, disrupting food chains and leading to mass extinction. Third, the fossil record reveals a gradual decline in dinosaur diversity in the millions of years before the impact. This pattern suggests that environmental deterioration caused by volcanism was already underway, weakening dinosaur populations before any possible asteroid strike. Therefore, while an asteroid may have delivered a final blow, the Deccan Traps volcanism was the dominant driver of the dinosaur extinction.
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The reading argues that volcanic activity was the main cause of dinosaur extinction, but this view is problematic. First, although the Deccan Traps eruptions began around 66 million years ago, their most intense phase actually occurred about 300,000 years before the extinction event. The extinction itself happened abruptly, coinciding with the asteroid impact, not with the peak volcanic activity. Thus, the timing does not support a volcanic cause. Second, the climate effects of volcanism are not as severe as the reading suggests. While volcanic gases can cause cooling or warming, the Deccan Traps eruptions were long-lasting and sustained, allowing ecosystems to gradually adapt. In contrast, an asteroid impact injects dust and aerosols into the stratosphere in a single event, causing a sudden and catastrophic drop in sunlight, which would have been far more disruptive. Third, the claim of a gradual dinosaur decline is not supported by recent high-resolution fossil studies. In many regions, dinosaur diversity remained high until the very end of the Cretaceous. The apparent decline in some records is likely due to sampling biases or incomplete preservation. Therefore, the evidence actually points to a sudden, impact-driven extinction rather than a volcanic one.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
