The Extinction of the Megafauna: A Climate-Driven Event
During the late Pleistocene, roughly 50,000 to 10,000 years ago, much of the world’s large terrestrial animals—such as mammoths, giant sloths, and saber-toothed cats—went extinct. While some scientists attribute these extinctions to human hunting, a closer examination of the evidence suggests that climate change was the primary driver. First, the timing of the extinctions aligns closely with known periods of rapid climate fluctuation, particularly the dramatic warming at the end of the last Ice Age. For example, in North America, the extinction of many megafauna species occurred around 13,000 years ago, exactly when the Younger Dryas cooling event brought abrupt shifts in temperature and vegetation. Second, the habitat preferences of these animals support a climate-driven explanation. Many megafauna, such as the woolly mammoth, were adapted to cold, dry steppe environments. As the climate warmed, these habitats shrank and were replaced by forests and wetlands, leaving the animals with insufficient food and shelter. Third, climate models and fossil pollen records show that plant communities underwent major reorganization during this period, which would have disrupted the entire food chain. These ecological upheavals likely stressed megafauna populations even before any human contact, making them vulnerable to extinction. Therefore, while human hunting may have played a minor role, climate change was the fundamental cause of megafaunal extinction.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
Now listen to a lecture on the same topic.
Professor: The reading argues that climate change was the main cause of megafaunal extinction, but this view is seriously flawed. Consider the timing. While it is true that some extinctions coincided with rapid climate shifts, many species disappeared thousands of years after the most severe climate changes. For instance, in Australia, megafauna went extinct around 45,000 years ago, long before the end of the last Ice Age, and at a time when climate was relatively stable. Similarly, on many islands, species survived major climate events only to vanish shortly after humans arrived. Second, the habitat argument is misleading. Even as grasslands converted to forests, megafauna were often generalists that could adapt to new environments. Fossil evidence shows that some species, like the giant deer, thrived in warmer periods. Moreover, if climate were the cause, we would expect a gradual decline across many species, but the fossil record shows a rapid, synchronous extinction that is more consistent with a sudden, widespread threat. Third, the ecological disruption cited in the reading actually supports human involvement. The arrival of skilled human hunters—who used advanced tools and fire to alter landscapes—would have caused rapid habitat fragmentation and overhunting, leading to the collapse of prey populations. In fact, archaeological sites containing spear points and butchered megafauna bones provide direct evidence of human predation. When we combine this with the fact that extinctions were most severe on continents where humans arrived later, it becomes clear that human activity, not climate, was the decisive factor.
📝 Writing Prompt Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
