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 in present-day India, was the primary cause. First, the timing of the Deccan Traps eruptions aligns closely with the extinction event. Geochemical dating shows that the main phase of volcanic activity occurred about 66 million years ago, coinciding with the Cretaceous-Paleogene boundary. This temporal correlation is too precise to be coincidental. Second, volcanic emissions of sulfur dioxide and carbon dioxide would have caused severe climate change, including rapid global cooling (volcanic winter) followed by long-term warming. Such dramatic temperature shifts would have stressed ecosystems worldwide, leading to the collapse of food chains before any asteroid impact. Third, the fossil record reveals a gradual decline in dinosaur diversity over the last few million years of the Cretaceous, suggesting that environmental deterioration caused by volcanism was already underway. This pattern contradicts the sudden extinction expected from an asteroid strike and supports a more protracted volcanic-driven demise.
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The reading's argument that volcanism alone caused dinosaur extinction is unconvincing. First, while the Deccan Traps began erupting around 66 million years ago, the most intense volcanic pulses actually occurred well before the extinction horizon, with a significant lull in activity in the final 200,000 years before the boundary. In contrast, the Chicxulub asteroid impact occurred precisely at the boundary, correlating directly with the mass extinction. Second, the climate effects of volcanic gases, though significant, were not severe enough to cause global extinction. Paleoclimate models indicate that Deccan eruptions produced intermittent cooling, but many species, including dinosaurs, had survived similar volcanic episodes earlier in the Cretaceous. The asteroid impact, however, ejected vast amounts of dust and sulfur, causing a sudden 'impact winter' that shut down photosynthesis for months—a far more catastrophic and rapid environmental disruption. Third, the claim of gradual dinosaur decline is based on incomplete fossil records. Recent high-resolution studies show that dinosaur diversity remained stable until the very end of the Cretaceous, and the apparent decline is an artifact of sampling biases. When corrected, the fossil record indicates sudden extinction, consistent with an asteroid impact. Thus, the impact remains the most plausible primary cause.
📝 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.
