The extinction of the dinosaurs at the end of the Cretaceous period has long been attributed to a massive asteroid impact. However, recent evidence suggests that volcanic activity, specifically the Deccan Traps eruptions in India, may have been the primary cause. This volcanic hypothesis is supported by three main arguments. First, the Deccan Traps eruptions lasted for over a million years, releasing enormous amounts of sulfur dioxide and carbon dioxide into the atmosphere. These gases would have caused severe global cooling and acid rain, disrupting photosynthesis and leading to a gradual decline in dinosaur populations long before the asteroid impact. Second, fossil records show a decline in dinosaur diversity in the 500,000 years preceding the impact, which aligns with the peak of volcanic activity. This gradual decline is inconsistent with a sudden asteroid-induced extinction. Third, the asteroid impact hypothesis struggles to explain why other species, such as crocodiles and birds, survived the event, whereas volcanic activity would have had a more gradual and selective effect, allowing adaptable species to survive. Therefore, the Deccan Traps volcanism, not the asteroid, was the dominant driver of the dinosaur extinction.
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The reading argues that volcanic activity caused dinosaur extinction, but this view is flawed. While the Deccan Traps did release gases, the timing does not match. The most intense volcanic phase occurred about 200,000 years before the impact, yet dinosaur fossils show stable populations during that period. The decline in diversity mentioned in the reading is actually an artifact of sampling bias—fewer fossils are found in layers close to the impact because of poor preservation conditions. Furthermore, the asteroid impact at Chicxulub released energy equivalent to billions of Hiroshima bombs, causing an immediate 'impact winter' that blocked sunlight for months, halting photosynthesis globally. This sudden catastrophe explains the rapid extinction of large land animals, including dinosaurs, while smaller, burrowing or aquatic species survived by buffering against the extreme temperature drop. In contrast, volcanic gases would have caused gradual changes, but dinosaurs had survived similar volcanic episodes for millions of years without going extinct. Thus, the asteroid impact remains the most plausible cause, and the volcanic hypothesis does not hold up under scrutiny.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
