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, specifically the Deccan Traps eruptions in India, was the primary cause. First, the timing of the Deccan Traps eruptions aligns closely with the extinction event. Radioisotopic dating shows that the main phase of volcanic activity occurred around 66 million years ago, exactly when the dinosaurs disappeared. This temporal correlation is too precise to be coincidental. Second, volcanic eruptions release vast amounts of sulfur dioxide and carbon dioxide, which can cause rapid climate change. The Deccan Traps would have emitted enough gases to create a volcanic winter followed by long-term global warming, stressing ecosystems and disrupting food chains long before any asteroid arrived. Third, the fossil record reveals a gradual decline in dinosaur diversity in the millions of years leading up to the extinction. This pattern is more consistent with a slow, ongoing environmental stressor like volcanism rather than a sudden catastrophic impact. Therefore, while an asteroid may have delivered a final blow, the Deccan Traps volcanism was the fundamental driver of the dinosaurs' demise.
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The reading's argument that Deccan Traps volcanism caused the dinosaur extinction is unconvincing. First, the timing argument is flawed. Although the main eruptions occurred near the extinction, high-precision dating now shows that the most intense phase of volcanic activity actually began about 200,000 years before the impact and ended roughly 100,000 years before the mass extinction. In contrast, the Chicxulub impact occurred precisely at the extinction boundary, within a margin of 30,000 years. The impact is the only event that matches the extinction moment exactly. Second, the climate effects of the Deccan Traps were likely less severe than proposed. Recent models indicate that the volcanic gases were emitted over hundreds of thousands of years, allowing the climate system to buffer the changes. Conversely, the asteroid impact injected dust, soot, and sulfur into the atmosphere in a matter of days, causing a sudden global darkness and cooling that would have shut down photosynthesis. No volcanic event can produce such a rapid and drastic change. Third, the claim of a gradual dinosaur decline is not supported by the latest fossil analyses. When corrected for sampling biases, dinosaur diversity remained stable until the very end of the Cretaceous. The apparent decline is an artifact of incomplete fossil records. Thus, the reading's evidence for volcanism fails, and the asteroid impact remains the most plausible 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.
