TOEFL統合ライティング

📖 読解文章

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 intense volcanic activity, specifically the Deccan Traps eruptions in modern-day India, was the primary cause. First, the timing of the Deccan Traps eruptions aligns closely with the extinction event, with the main phase of volcanic activity occurring just before and at the boundary. This temporal correlation is too precise to be coincidental, suggesting a causal link. Second, volcanic eruptions released vast amounts of sulfur dioxide and carbon dioxide, leading to severe climate fluctuations, including rapid global warming and cooling, which would have stressed ecosystems worldwide. This is consistent with the fossil record showing gradual declines in dinosaur diversity and other species well before the asteroid impact. Third, the Deccan Traps eruptions produced enough lava to cover an area the size of Texas, and the associated toxic gases and particulates would have caused long-term environmental poisoning, including acid rain and ozone depletion, making the planet inhospitable for large reptiles. Thus, while the asteroid may have delivered the final blow, the volcanic activity was the dominant driver of the end-Cretaceous mass extinction.

🎧 リスニング講義

The reading's argument for volcanic activity as the primary cause of dinosaur extinction is flawed. While it is true that the Deccan Traps eruptions occurred around the same time as the extinction, the most intense phase of volcanism actually began about 300,000 years before the impact event and had largely subsided by the time of the asteroid strike. The last and most lethal phase of eruptions coincided with the impact itself, but the massive and sudden environmental effects of the asteroid—such as global wildfires, a dust cloud blocking sunlight for months, and a subsequent impact winter—are far more consistent with the abrupt extinction pattern seen in the fossil record. In contrast, volcanic activity would have caused a more gradual extinction, yet the fossil record shows that many species, including dinosaurs, existed in high numbers right up until the impact boundary, contradicting the claim of gradual decline. Furthermore, the sulfur and carbon dioxide released by volcanoes, while significant, are comparable to those from the asteroid's vaporization of sulfate-rich rocks, but the asteroid delivered this in a matter of seconds, overwhelming the climate system in a way that sustained volcanic output could not. Therefore, the unique and catastrophic signature of the impact better explains the sudden and selective extinction.