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托福TPO39综合写作阅读原文文本： At the end of the Triassic period 200 million years ago, there was a mass-extinction event that caused the extinction of more than half of all living species. It was this extinction event that allowed dinosaurs to become the dominant species for the next 145 million years. We do not know exactly what happened that eliminated so many species in a relatively short period of time, but there are several possible explanations.One theory involves the decline of sea levels. Near the end of the Triassic period, sea levels were fluctuating. When sea levels fall, the habitats for ocean populations that live in the shallows and land species that live on the coast are destroyed. The destruction of coastal and shallow-ocean species would have had a profound effect on food chains worldwide, leading to mass extinctions.Another theory involves massive climate cooling. The end of the Triassic period was marked by widespread volcanic activity. The volcanoes released large amounts of sulfur dioxide (S02). A rise in atmospheric S02 is known to cause a lowering in global temperatures. Such climate change could have devastated many species and led to the extinctions.The third theory involves an asteroid strike. Asteroids (objects from outer space) occasionally collide with Earth. When an asteroid hits Earth’s surface, it often displaces large amounts of soil and crushed rock, leaving behind a depression, or crater. The displaced debris is thrown up into the atmosphere where it can block out sunlight for many months or even a few years. A sufficiently massive asteroid impact at the end of the Triassic period may have blocked sunlight long enough for most plants to die and many animal species to then starve. 托福TPO39综合写作听力原文文本： Well the theories given in the reading may sound plausible, none of them is a good explanation for the massive extinction at the end of the Triassic period. First, sea level change. Well scientists agree that the sea level fluctuated at the end of the Triassic period often going down. This isn’t a good explanation for the extinctions. Coastal and shallow water ecosystems are usually capable of adapting to environmental changes that happen gradually. The falling sea level at the end of the Triassic period was quite gradual, taking place over several million years. The change would have to be much more sudden to have a widespread negative impact on the species in those ecosystems.Second, global cooling. It’s true that sulfur dioxide can lower global temperatures, but that can only happen during a relatively short period, when the sulfur dioxide that’s been released by volcanoes is actually still present in the atmosphere. In a matter of a few years, the excess SO2 is usually cleared out of the atmosphere. Basically, the SO2 combines with water in the atmosphere, and falls back on earth as rain. It doesn’t seem likely, therefore, that even if there was a lot of volcanic SO2 released at the end of the Triassic, it stayed in theatmosphere long enough to cause mass distinctions.Third, very few scientists believe the asteroid theory because we haven’t found any asteroid crater the side where the asteroid hit that can be dated to the time when the mass distinction occurred. We did find a crater, but it dates to about 12 million years before the extinction. That’s just too long before the extinction to have anything to do with it. 托福TPO39综合写作满分范文： This set of material focus on the debate over explanations about mass-extinction event. The author proposes three possible theories but the speaker retorts them one by one. First, the passage says that the decline of sea level will cause coast species to distinct and thus lead to the elimination of other species. However, the lecturer indicates that sea level indeed fluctuates during this period, but it actually goes down at a very low speed. This change takes millions of years. The period is so long that it is certainly enough time for earth species to adapt themselves to it. Therefore, the first idea of the essay is rebutted. Second, the author demonstrated that frequent volcanic activity will release too much sulfur dioxide which can lead to earth cooling. Nevertheless, the speaker argues that sulfur dioxide presents for few years in earth’s atmosphere, but it can combine with water and become rain. Consequently, the sulfur dioxide leaves the air so it is impossible for it to stay long enough in the atmosphere and cause apparent temperature drop. Third, the writer holds that asteroids collide with the earth produces large amounts of debris which block sunlight, finally leading to the death of plantations and the starvation of animals. While the speaker says that it is found the asteroid strike happened about 12 million years before the mass-extinction. It is too long before the sudden elimination of earth species so probably has nothing to do with this great collision. Thus overturns the third viewpoint in the essay. (254 words) 以上是给大家整理的托福TPO39综合写作阅读原文+听力原文+满分范文，希望对你有所帮助!。