托福综合写作

📖 阅读文章

The extinction of the dinosaurs at the end of the Cretaceous period, about 66 million years ago, has long fascinated scientists. While the asteroid impact theory is widely accepted, a competing hypothesis suggests that massive volcanic eruptions in the Deccan Traps of India were the primary cause. This volcanic theory is supported by three main arguments. First, the Deccan Traps eruptions were prolonged, lasting for over a million years, and would have released enormous quantities of sulfur dioxide and carbon dioxide. These gases could have caused severe global cooling (via sulfate aerosols) followed by long-term warming (via CO2), creating drastic climate instability that stressed ecosystems long before any asteroid hit. Second, fossils show a gradual decline in dinosaur diversity and population sizes in the millions of years leading up to the Cretaceous-Paleogene (K-Pg) boundary, which aligns with the slow, cumulative effects of volcanic activity rather than a sudden impact. Third, the timing of the most intense volcanic phase appears to coincide with the K-Pg boundary, suggesting that the eruptions—not the asteroid—delivered the final, fatal blow to the dinosaurs. Thus, volcanism alone may explain the extinction without invoking an extraterrestrial event.

🎧 听力讲座

The lecture challenges the volcanic theory presented in the reading. While the Deccan Traps eruptions were indeed massive, their timescale is a problem. The reading argues for a gradual decline, but recent high-resolution fossil studies show that dinosaur diversity remained stable until the very end of the Cretaceous, with no significant decline over millions of years. This contradicts the volcanic model, which would predict a slow decline. Furthermore, the timing of the main volcanic phase is not as precise as claimed. Geochronological data indicate that the most intense eruptions occurred about 250,000 years before the K-Pg boundary, not exactly at it. This gap suggests that volcanic effects alone were insufficient to cause extinction, as ecosystems partially recovered before the boundary. Finally, the reading overlooks the distinct chemical signature of the boundary layer, which contains high levels of iridium and shocked quartz—materials typical of an asteroid impact, not volcanic eruptions. These markers are found globally at the exact extinction horizon, providing a clear, immediate cause that volcanism cannot replicate. Therefore, the asteroid impact remains the most compelling explanation for the dinosaurs' demise.