TOEFL 통합 작문

📖 읽기 지문

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 in the Deccan Traps of India was the primary cause. First, the timing of the Deccan eruptions aligns closely with the extinction event. Radioisotopic dating places the main phase of volcanic activity at 66 million years ago, exactly when the dinosaurs disappeared. Second, volcanic gases such as sulfur dioxide and carbon dioxide would have caused rapid climate fluctuations—initial cooling from sulfate aerosols followed by long-term warming from CO2—creating severe stress on ecosystems. This is consistent with the fossil record, which shows a gradual decline in dinosaur diversity over the last few hundred thousand years before the extinction, rather than a sudden die-off. Third, the asteroid impact theory has a critical flaw: the Chicxulub crater in Mexico is dated to 66 million years ago, but many dinosaur fossils are found below the impact layer, suggesting they went extinct before the impact. Therefore, volcanic activity, not an asteroid, was the main driver of the Cretaceous-Paleogene extinction.

🎧 듣기 강의

The lecture challenges the idea that volcanic activity caused the dinosaur extinction. While the Deccan eruptions were massive, their timing does not match the extinction as precisely as the reading claims. High-resolution dating shows that the most intense volcanic phase occurred about 300,000 years before the impact, and the final, smaller eruptions after the impact were not sufficient to cause a global catastrophe. In fact, the fossil record reveals that dinosaur diversity was relatively stable until the very end of the Cretaceous, contradicting the claim of a gradual decline. The apparent decline in some fossil assemblages is likely due to sampling bias—fewer sedimentary layers from that period are preserved. Furthermore, the reading's point about dinosaur fossils below the impact layer is misleading. These fossils are found in sediments that predate the impact by tens of thousands of years, but they do not indicate extinction before the impact; rather, they simply show that dinosaurs lived right up to the impact horizon. The Chicxulub impact, on the other hand, released energy equivalent to billions of Hiroshima bombs, causing global wildfires, a dust cloud that blocked photosynthesis, and a subsequent collapse of food chains. These abrupt effects are far better aligned with the sudden extinction seen in the fossil record. Thus, the impact, not volcanism, remains the most credible cause.