托福综合写作

📖 阅读文章

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 India, was the primary driver. First, the timing of the Deccan Traps eruptions coincides with the extinction event. Radioisotopic dating places the main phase of eruptions at approximately 66 million years ago, exactly when the dinosaur fossils disappear from the rock record. This temporal correlation is too precise to be coincidental. Second, volcanic emissions would have caused severe environmental stress. The Deccan Traps released enormous quantities of sulfur dioxide and carbon dioxide, leading to acid rain, global cooling followed by warming, and ocean acidification. These changes would have disrupted food chains and habitats, gradually pushing many species to extinction. Third, the fossil record shows a gradual decline in dinosaur diversity well before the asteroid impact. In the last few hundred thousand years of the Cretaceous, dinosaur fossils become increasingly rare and less diverse, suggesting that populations were already struggling due to volcanic-induced environmental changes. The asteroid impact, while catastrophic, likely only delivered the final blow to already vulnerable ecosystems.

🎧 听力讲座

The lecture challenges the volcanic hypothesis, arguing that the asteroid impact is the more plausible cause. 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 eruptions had largely subsided by the time of the mass extinction, so their environmental effects would have waned. In contrast, the Chicxulub impact happened exactly at the boundary, matching the extinction precisely. Second, volcanic emissions, while substantial, are not sufficient to explain the rapid and selective nature of the extinction. The impact would have caused a sudden global winter, darkness, and wildfires, wiping out photosynthetic organisms and then herbivores and carnivores in a matter of months. Volcanic activity, on the other hand, operates over millennia, giving species time to adapt. Third, the claim of a gradual dinosaur decline is misleading. The apparent decrease in fossil diversity may be due to sampling bias, as rock layers from that time are scarce. When corrected for sampling, dinosaur diversity remained high until the very end. Thus, the lecture concludes that the asteroid impact, not volcanism, was the decisive factor.