Irma

托福閱讀 練習小短文 - 恐龍滅絕(古生物學科) 

這是一篇有關解釋恐龍滅絕的文章，大家可能對恐龍滅絕的原因可能略有所知，但詳細內容未必深入了解，所以想要了解整篇文章單字就變的很重要，從以下單字可以約略得知整篇文章的單字其實也不是很容易，因為其實不單單是生物學科，另外可能也包含地理學科，也可以由此得知為什麼在準備托福的關鍵之一就是單字量，沒有足夠的單字量是無法考好托福。

基本單字

1) Paleontologist 古生物學家

2) argued (V.) 爭論；爭吵；爭辯；論證；說理；辯論；顯示出；表明

3) demise (V.) 死亡，逝世；倒閉；敗落；垮臺

4) dinosaur (N.) 恐龍；老古董

5) alteration  (N.)（通常指輕微地）改動，修改；改變，（使）變化；變化（過程）

6) associate  (V.) 將…（與…）聯繫起來，把…聯繫在一起

7) continent  (N.) 洲，大洲，大陸

8) result from sth 因…發生，由於…導致

9) plate tectonics  板塊運動

10) Cretaceous 白堊紀

11) Mesozoic era 中生代

12) flourish  (V.) 茁壯成長；繁榮；蓬勃發展；（為引人注意）揮舞

13) shallow (Adj.) 淺的，不深的；膚淺的，淺薄的

14) extensive (Adj.) 廣闊的，大面積的；覆蓋範圍廣的

15) geochemical　(Adj.) 地球化學的

Paleontologists have argued for a long time that the demise of the dinosaurs was caused by climatic alterations associated with slow changes in the positions of continents and seas resulting from plate tectonics. Off and on throughout the Cretaceous (the last period of the Mesozoic era, during which dinosaurs flourished), large shallow seas covered extensive areas of the continents. Data from diverse sources, including geochemical evidence preserved in seafloor sediments, indicate that the Late Cretaceous climate was milder than today’s. The days were not too hot, nor the nights too cold. The summers were not too warm, nor the winters too frigid. The shallow seas on the continents probably buffered the temperature of the nearby air, keeping it relatively constant.        

At the end of the Cretaceous, the geological record shows that these seaways retreated from the continents back into the major ocean basins. No one knows why. Over a period of about 100,000 years, while the seas pulled back, climates around the world became dramatically more extreme: warmer days, cooler nights; hotter summers, colder winters. Perhaps dinosaurs could not tolerate these extreme temperature changes and became extinct.      

If true, though, why did cold-blooded animals such as snakes, lizards, turtles, and crocodiles survive the freezing winters and torrid summers? These animals are at the mercy of the climate to maintain a livable body temperature. It’s hard to understand why they would not be affected, whereas dinosaurs were left too crippled to cope, especially if, as some scientists believe, dinosaurs were warm-blooded. Critics also point out that the shallow seaways had retreated from and advanced on the continents numerous times during the Mesozoic, so why did the dinosaurs survive the climatic changes associated with the earlier fluctuations but not with this one? Although initially appealing, the hypothesis of a simple climatic change related to sea levels is insufficient to explain all the data.      

  Dissatisfaction with conventional explanations for dinosaur extinctions led to a surprising observation that, in turn, has suggested a new hypothesis. Many plants and animals disappear abruptly from the fossil record as one moves from layers of rock documenting the end of the Cretaceous up into rocks representing the beginning of the Cenozoic (the era after the Mesozoic).Between the last layer of Cretaceous rock and the first layer of Cenozoic rock, there is often a thin layer of clay. Scientists felt that they could get an idea of how long the extinctions took by determining how long it took to deposit this one centimeter of clay and they thought they could determine the time it took to deposit the clay by determining the amount of the element iridium (lr) it contained.      

It has not been common at Earth’s since the very beginning of the planet’s history. Because it usually exists in a metallic state, it was preferentially incorporated in Earth’s core as the planet cooled and consolidated. It is found in high concentrations in some meteorites, in which the solar system’s original chemical composition is preserved. Even today, microscopic meteorites continually bombard Earth, falling on both land and sea. By measuring how many of these meteorites fall to Earth over a given period of time, scientists can estimate how long it might have taken to epos it the observed amount of lr in the boundary clay. These calculations suggest that a period of about one million years would have been required. However, other reliable evidence suggests that the deposition of the boundary clay could not have taken one million years. So the unusually high concentration of lr seems to require a special explanation.      

In view of these facts, scientists hypothesized that a single large asteroid, about 10 to 15 kilometers across, collided with Earth, and the resulting fallout created the boundary clay. Their calculations show that the impact kicked up a dust cloud that cut off sunlight for several months, inhibiting photosynthesis in plants; decreased surface temperatures on continents to below freezing; caused extreme episodes of acid rain; and significantly raised long-term global  temperatures through the greenhouse effect. This disruption of food chain and climate would have eradicated the dinosaurs and other organisms in less than fifty years.