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 extensive volcanic activity, specifically the Deccan Traps in India, was the primary driver. First, volcanic eruptions release vast amounts of sulfur dioxide and carbon dioxide, which can cause rapid climate change. The Deccan Traps eruptions, spanning over a million years, would have produced enough aerosols to block sunlight, causing a global cooling that disrupted photosynthesis and food chains. Second, the timing of the Deccan Traps aligns precisely with the extinction event. Radiometric dating shows that the main phase of eruptions began about 66 million years ago, coinciding with the Cretaceous-Paleogene boundary, whereas the Chicxulub impact occurred slightly earlier, allowing for a lag period. Third, volcanic activity leads to ocean acidification due to increased CO2 absorption, which would have devastated marine life, including plankton and shelled organisms. This is consistent with the fossil record showing a gradual decline in marine biodiversity leading up to the extinction, rather than a sudden die-off expected from an impact.

🎧 듣기 강의

The professor argues that the volcanic hypothesis is flawed, and the asteroid impact remains the most compelling explanation. First, while volcanic aerosols can cause cooling, the Deccan Traps eruptions also released massive amounts of CO2, a greenhouse gas, which would have caused long-term warming. The cooling effect would be temporary, whereas the extinction was abrupt and followed by a prolonged period of darkness, consistent with an impact winter. Second, the professor points out that the precise timing of the Deccan Traps is problematic. Although eruptions began around 66 million years ago, the most intense volcanic activity occurred hundreds of thousands of years after the extinction boundary, not exactly at it. In contrast, the Chicxulub impact is dated to within 30,000 years of the boundary, making it a more synchronous event. Third, the claim of gradual marine decline is unsupported. The fossil record shows that marine plankton experienced a sudden and catastrophic collapse at the boundary, with no evidence of a prior gradual loss. Additionally, the impact would have caused ocean acidification through nitrogen oxides and sulfate aerosols, not just CO2, explaining the selective extinction of shell-bearing organisms. Thus, the lecture casts doubt on each volcanic claim.