『新东方在线托福阅读』为托福考生准备了ETS托福TPO/Official 8 Passage 2阅读练习：Paragraph 5 implies that a special explanation of the Ir in the boundary clay is needed because真题题目及答案解析，TPO/Official 8 Passage 2阅读原文范文音频翻译

托福TPO/Official 8 Passage 2阅读原文Paragraph 5 implies that a special explanation of the Ir in the boundary clay is needed because题目答案及解析-新东方托福官方网校手机版

古生物学家长期以来一直认为，恐龙的灭绝是由气候变化引起的，气候变化与板块构造导致的大陆和海洋位置的缓慢变化有关。

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.

在整个白垩纪（中生代的最后一个时期，也是恐龙繁荣的一个时期），大片浅海覆盖了广阔陆地。

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.

不同来源的数据，包括海底沉积物地质化学证据，表明白垩纪晚期的气候比现在更温和。

Data from diverse sources, including geochemical evidence preserved in seafloor sediments, indicate that the Late Cretaceous climate was milder than today’s.

那时候白天不太热，晚上也不太冷。

The days were not too hot, nor the nights too cold.

The summers were not too warm, nor the winters too frigid.

陆地上的浅海稳定了周围空气的温度，让温度比较稳定。

The shallow seas on the continents probably buffered the temperature of the nearby air, keeping it relatively constant.

地质记录表明在白垩纪晚期这些海道从陆地上消失了，退回到了主要的海洋盆地里。

At the end of the Cretaceous, the geological record shows that these seaways retreated from the continents back into the major ocean basins.

在10万年间，海洋收缩，全球气候变得极端：白天更暖和，晚上更冷；夏天更热，冬天更冷。

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.

可能恐龙无法适应这些极端的天气变化，因此就灭绝了。

Perhaps dinosaurs could not tolerate these extreme temperature changes and became extinct.

然而，如果真是这样的话，其他冷血动物，比如蛇、蜥蜴、乌龟与鳄鱼是如何在寒冷的冬天与酷热的夏天里存活下来的？

If true, though, why did cold-blooded animals such as snakes, lizards, turtles, and crocodiles survive the freezing winters and torrid summers?

这些动物依靠气候来维持适宜生存的体温。

These animals are at the mercy of the climate to maintain a livable body temperature.

很难理解为什么它们不受到影响，而恐龙却无法应对这种变化，特别是很多科学家认为恐龙是恒温动物。

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.

评论家们指出在中生代浅海多次在陆地上出现与后退，所以为什么恐龙在历经了多次与海洋消退有关的气候波动后都存活了下来，然而这次却灭亡了？

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?

尽管看似有说服力，仅仅因为气候变化引起的海平面上升或下降这种假设不足以解释所有的数据。

Although initially appealing, the hypothesis of a simple climatic change related to sea levels is insufficient to explain all the data.

对恐龙灭绝的传统解释不满意，人们接着研究有了惊人发现，从而提出了一个新假设。

Dissatisfaction with conventional explanations for dinosaur extinctions led to a surprising observation that, in turn, has suggested a new hypothesis.

当人们研究白垩纪晚期岩石地层与新生代（中生代之后一个时期）初期岩石地层时，他们发现很多植物与动物突然从化石记录上消失了。

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).

在白垩纪岩石的最后一层与新生代岩石的第一层中间有一层薄薄的粘土。

Between the last layer of Cretaceous rock and the first layer of Cenozoic rock, there is often a thin layer of clay.

科学家们觉得可以通过研究一厘米粘土沉积下来的时间来确定灭绝所用时间。他们认为可以通过铱元素含量来确定粘土沉积物形成的时间。

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 (Ir) it contained.

在地球历史最初期，铱在地球表面并不常见。

Ir has not been common at Earth’s surface since the very beginning of the planet’s history.

因为它通常是金属形态，当地球变冷凝固的时候它融合到了地核里。

Because it usually exists in a metallic state, it was preferentially incorporated in Earth’s core as the planet cooled and consolidated.

很多陨石富含铱元素，太阳系很多原始化学成分都在陨石里保存了下来。

Ir is found in high concentrations in some meteorites, in which the solar system’s original chemical composition is preserved.

甚至现在，小陨石还在不停地袭击地球，掉落到陆地上与大海里。

Even today, microscopic meteorites continually bombard Earth, falling on both land and sea.

通过计算一段时期内掉落到地球上的陨石的数量，科学家可以估算界线粘土层里铱元素的形成用时。

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 deposit the observed amount of Ir in the boundary clay.

计算表明需要长达一百万年的时间。

These calculations suggest that a period of about one million years would have been required.

然而，其他可靠证据表明界线粘土的沉积不可能用一百万年。

However, other reliable evidence suggests that the deposition of the boundary clay could not have taken one million years.

因此，不同寻常的高含量铱元素看来需要一个特殊解释。

So the unusually high concentration of Ir seems to require a special explanation.

鉴于这些事实，科学家假设一个直径10-15公里的较大小行星与地球相撞了，随之而来的放射性尘埃形成了界线粘土。

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.

他们推测，撞击力使得尘埃上扬，形成尘埃云，一连几个月遮挡了阳光。因此，植物无法进行光合作用，陆地表面温度降到零度以下，酸雨不时来袭，并且通过温室效应导致全球温度长期上升。

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.

食物链与气候的紊乱用了不到50年就消灭了恐龙及其它生物。

This disruption of food chain and climate would have eradicated the dinosaurs and other organisms in less than fifty years.

According to paragraph 1, which of the following is true of the Late Cretaceous climate?

Which of the following reasons is suggested in paragraph 2 for the extinction of the dinosaurs?

Why does the author mention the survival of “snakes, lizards, turtles, and crocodiles” in paragraph 3?

The word “cope” in the passage is closest in meaning to

According to paragraph 3, which of the following is true of changes in climate before the Cretaceous period and the effect of these changes on dinosaurs?

The word “fluctuations” in the passage is closest in meaning to

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

In paragraph 4, all the following questions are answered EXCEPT:

The word “bombard” in the passage is closest in meaning to

Paragraph 5 implies that a special explanation of the Ir in the boundary clay is needed because

The word “disruption” in the passage is closest in meaning to

Paragraph 6 mentions all of the following effects of the hypothesized asteroid collision EXCEPT

Look at the four squares  that indicate where the following sentence could be added to the passage. Consequently, the idea that the Ir in the boundary clay came from microscopic meteorites cannot be accepted.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Extinction of the Dinosaurs 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 (Ir) it contained. Ir has not been common at Earth’s surface 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. Ir 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 deposit the observed amount of Ir 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 Ir 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.