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 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 mass extinction event. Radiometric dating shows that the main phase of volcanic activity occurred around 66 million years ago, coinciding with the Cretaceous-Paleogene boundary. Second, volcanic eruptions release vast amounts of sulfur dioxide and carbon dioxide, which can cause rapid climate change. The Deccan Traps would have produced enough gases to trigger global cooling and ocean acidification, leading to the collapse of ecosystems. Third, the fossil record reveals a gradual decline in dinosaur diversity well before the proposed asteroid impact, suggesting that environmental stress from volcanism was already taking its toll. This gradual pattern is more consistent with prolonged volcanic activity than with a sudden catastrophic impact.

🎧 リスニング講義

The professor argues that the reading’s claim about volcanism as the main cause of dinosaur extinction is flawed. 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 largest pulse of volcanic activity ended well before the mass die-off, and a later, smaller eruption phase does not match the abruptness of the extinction. Second, the climate effects of the Deccan Traps were likely not as severe as the reading suggests. Recent models indicate that while sulfur dioxide caused short-term cooling, the overall warming from carbon dioxide may have been moderate, and many species survived these fluctuations. The real killer was the asteroid impact, which threw up dust and aerosols, blocking sunlight for months and causing a sudden, catastrophic collapse. Third, the fossil record does not support a gradual decline. High-resolution studies of dinosaur fossils show that dinosaurs were thriving right up to the impact layer, with no evidence of a prolonged decline. The apparent gradual pattern in older studies was an artifact of incomplete sampling. Therefore, the asteroid impact remains the most plausible explanation.