『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 20 Passage 3阅读练习，TPO/Official 20 Passage 3原文答案解析，TPO/Official 20 Passage 3阅读原文练习音频翻译。

托福TPO/Official 20 Passage 3阅读原文题目答案及解析-新东方托福官方网校手机版

考虑到生物体在死亡之后以多种形式被完全破坏，化石的常见性就显得引人注意。

When one considers the many ways by which organisms are completely destroyed after death, it is remarkable that fossils are as common as they are.

来自食腐动物和细菌的损害、化学性腐烂、侵蚀以及其他地质作用的破坏都提升了被保存下来的难度。

Attack by scavengers and bacteria, chemical decay, and destruction by erosion and other geologic agencies make the odds against preservation very high.

然而，如果该生物体恰巧拥有矿化骨骼并且死在了可以被沉积物迅速掩埋的地方，那么逃脱被完全摧毁的可能性就大幅提升。

However, the chances of escaping complete destruction are vastly improved if the organism happens to have a mineralized skeleton and dies in a place where it can be quickly buried by sediment.

海底通常具备这两方面的条件，带壳的无脊椎动物（没有脊椎的生物体）在此繁衍生息，沉积颗粒如连绵不断的阴雨会把它们掩埋起来。

Both of these conditions are often found on the ocean floors, where shelled invertebrates (organisms without spines) flourish and are covered by the continuous rain of sedimentary particles.

尽管大部分化石是在海洋沉积岩中所发现的，但是在溪流和湖泊留下的陆地沉积物中也发现过化石。

Although most fossils are found in marine sedimentary rocks, they also are found in terrestrial deposits left by streams and lakes.

浸入焦油或流沙、陷入冰或岩浆流或者被急速降落的火山灰所吞没的动物和植物偶尔也能被保存下来。

On occasion, animals and plants have been preserved after becoming immersed in tar or quicksand, trapped in ice or lava flows, or engulfed by rapid falls of volcanic ash.

术语“化石”一词通常意味着石化，字面意思就是转化为石头。

The term “fossil” often implies petrifaction, literally a transformation into stone.

生物体死后，软组织通常会被食腐动物和细菌吃掉。

After the death of an organism, the soft tissue is ordinarily consumed by scavengers and bacteria.

蜗牛或蛤蜊的空壳或许会被留下，如果空壳足够耐久并且能够抵抗分解的话，就有可能在长时间内基本保持不变。

The empty shell of a snail or clam may be left behind, and if it is sufficiently durable and resistant to dissolution, it may remain basically unchanged for a long period of time.

事实上，已知的在沉积物中发现的保存良好的海洋无脊椎动物的壳已超过了1亿年。

Indeed, unaltered shells of marine invertebrates are known from deposits over 100 million years old.

然而，许多海洋生物的骨骼是由称为霰石的多种碳酸钙矿物质所构成的。

In many marine creatures, however, the skeleton is composed of a mineral variety of calcium carbonate called aragonite.

尽管霰石与更为人们所熟知的矿物方解石拥有相同的成分，但是霰石的晶体形式不同，相对不稳定，并会适时地变成更加稳定的方解石。

Although aragonite has the same composition as the more familiar mineral known as calcite, it has a different crystal form, is relatively unstable, and in time changes to the more stable calcite.

很多其他过程可能会改变蛤蜊或蜗牛的壳，并增加它被保存下来的机会。

Many other processes may alter the shell of a clam or snail and enhance its chances for preservation.

含有溶解了的二氧化硅、碳酸钙或铁的水流可能会流经封闭的沉积物，并被储存到例如骨髓腔和骨髓管内部，这些地方曾经被血管和神经所占据。

Water containing dissolved silica, calcium carbonate, or iron may circulate through the enclosing sediment and be deposited in cavities such as marrow cavities and canals in bone once occupied by blood vessels and nerves.

在这种情况下，骨骼或贝壳的原始构成得以保留，但是所形成的化石则变得更加坚硬且持久。

In such cases, the original composition of the bone or shell remains, but the fossil is made harder and more durable.

在孔隙中填充化学沉积物质的过程被称为“完全矿化”。

This addition of a chemically precipitated substance into pore spaces is termed “permineralization.”

石化同样会涉及已死亡的植物或动物的原有物质与不同成分的矿物质的同时交换。

Petrifaction may also involve a simultaneous exchange of the original substance of a dead plant or animal with mineral matter of a different composition.

由于溶液溶解了原有物质并将其替换为同样体积的新物质，因此这一过程被称为“置换”。

This process is termed “replacement” because solutions have dissolved the original material and replaced it with an equal volume of the new substance.

置换是一个不可思议的精确过程，贝壳纹路的细节、树木的年轮以及骨骼里的精细结构都被准确地保存下来。

Replacement can be a marvelously precise process, so that details of shell ornamentation, tree rings in wood, and delicate structures in bone are accurately preserved.

另一种被称为“碳化”的石化会把软组织以碳薄膜的形式保存下来。

Another type of fossilization, known as carbonization, occurs when soft tissues are preserved as thin films of carbon.

叶片和软体生物例如水母或蠕虫的组织会积聚起来，逐渐被掩埋并压实，其中的易挥发成分会消失。

Leaves and tissue of soft-bodied organisms such as jellyfish or worms may accumulate, become buried and compressed, and lose their volatile constituents.

碳通常会以一种黑色轮廓被保留下来。

The carbon often remains behind as a blackened silhouette.

拥有坚硬的部分确实增加了被保存下来的可能性，但是拥有软组织和器官的生物体偶尔也能被保存下来。

Although it is certainly true that the possession of hard parts enhances the prospect of preservation, organisms having soft tissues and organs are also occasionally preserved.

昆虫甚至是小型无脊椎动物被发现保存于松柏类和某些其他树木的凝固树脂之中。

Insects and even small invertebrates have been found preserved in the hardened resins of conifers and certain other trees.

对岩石薄板的X射线检查有时会发现一些影子般的轮廓，这些是多种海洋生物的触须、消化道和视觉器官。

X-ray examination of thin slabs of rock sometimes reveals the ghostly outlines of tentacles, digestive tracts, and visual organs of a variety of marine creatures.

冰河世纪猛犸象的软组织（包括皮肤、毛发和内脏）被保存在冻土或石油泄漏时所渗出的焦油之中。

Soft parts, including skin, hair, and viscera of ice age mammoths, have been preserved in frozen soil or in the oozing tar of oil seeps.

如果生物体死在一个迅速沉积且缺氧的环境之中，那么就会提高软组织残余物被保存的可能性。

The probability that actual remains of soft tissue will be preserved is improved if the organism dies in an environment of rapid deposition and oxygen deprivation.

在这种条件下，细菌的破坏作用会被减少。

Under such conditions, the destructive effects of bacteria are diminished.

来自德国的始新世中期的梅塞尔页岩（来自大约4800万年前）就是在这种环境下积聚下来的。

The Middle Eocene Messel Shale (from about 48 million years ago) of Germany accumulated in such an environment.

该页岩沉积在一个缺氧的湖泊里，从湖中冒出的有毒气体有时会杀死动物。

The shale was deposited in an oxygen-deficient lake where lethal gases sometimes bubbled up and killed animals.

动物的残骸在湖底逐渐增加，然后被粘土和淤泥所覆盖。

Their remains accumulated on the floor of the lake and were then covered by clay and silt.

在这些完好保存的梅塞尔化石中，有色彩斑斓的带有外骨骼（坚硬的外壳）的昆虫，皮肤和血管完整的青蛙，甚至还有毛皮和软组织都保存下来的完整的小型哺乳动物。

Among the superbly preserved Messel fossils are insects with iridescent exoskeletons (hard outer coverings), frogs with skin and blood vessels intact, and even entire small mammals with preserved fur and soft tissue.

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

In paragraph 1, what is the author’s purpose in providing examples of how organisms are destroyed?

The word “terrestrial” 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.

Why does the author mention “aragonite” in the passage?

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

Which of the following best explains the process of permineralization mentioned in paragraph 3?

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

Paragraph 5 suggests which of the following about the carbonization process?

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

According to paragraph 7, how do environments containing oxygen affect fossil preservation?

According to the passage, all of the following assist in fossil preservation EXCEPT

Look at the four squares  that indicate where the following sentence could be added to the passage. But the evidence of past organic life is not limited to petrifaction.  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.

Fossil Preservation When one considers the many ways by which organisms are completely destroyed after death, it is remarkable that fossils are as common as they are. Attack by scavengers and bacteria, chemical decay, and destruction by erosion and other geologic agencies make the odds against preservation very high. However, the chances of escaping complete destruction are vastly improved if the organism happens to have a mineralized skeleton and dies in a place where it can be quickly buried by sediment. Both of these conditions are often found on the ocean floors, where shelled invertebrates (organisms without spines) flourish and are covered by the continuous rain of sedimentary particles. Although most fossils are found in marine sedimentary rocks, they also are found in terrestrial deposits left by streams and lakes. On occasion, animals and plants have been preserved after becoming immersed in tar or quicksand, trapped in ice or lava flows, or engulfed by rapid falls of volcanic ash. The term “fossil” often implies petrifaction, literally a transformation into stone. After the death of an organism, the soft tissue is ordinarily consumed by scavengers and bacteria. The empty shell of a snail or clam may be left behind, and if it is sufficiently durable and resistant to dissolution, it may remain basically unchanged for a long period of time. Indeed, unaltered shells of marine invertebrates are known from deposits over 100 million years old. In many marine creatures, however, the skeleton is composed of a mineral variety of calcium carbonate called aragonite. Although aragonite has the same composition as the more familiar mineral known as calcite, it has a different crystal form, is relatively unstable, and in time changes to the more stable calcite. Many other processes may alter the shell of a clam or snail and enhance its chances for preservation. Water containing dissolved silica, calcium carbonate, or iron may circulate through the enclosing sediment and be deposited in cavities such as marrow cavities and canals in bone once occupied by blood vessels and nerves. In such cases, the original composition of the bone or shell remains, but the fossil is made harder and more durable. This addition of a chemically precipitated substance into pore spaces is termed “permineralization.” Petrifaction may also involve a simultaneous exchange of the original substance of a dead plant or animal with mineral matter of a different composition. This process is termed “replacement” because solutions have dissolved the original material and replaced it with an equal volume of the new substance. Replacement can be a marvelously precise process, so that details of shell ornamentation, tree rings in wood, and delicate structures in bone are accurately preserved.  Another type of fossilization, known as carbonization, occurs when soft tissues are preserved as thin films of carbon.  Leaves and tissue of soft-bodied organisms such as jellyfish or worms may accumulate, become buried and compressed, and lose their volatile constituents.  The carbon often remains behind as a blackened silhouette.  Although it is certainly true that the possession of hard parts enhances the prospect of preservation, organisms having soft tissues and organs are also occasionally preserved. Insects and even small invertebrates have been found preserved in the hardened resins of conifers and certain other trees. X-ray examination of thin slabs of rock sometimes reveals the ghostly outlines of tentacles, digestive tracts, and visual organs of a variety of marine creatures. Soft parts, including skin, hair, and viscera of ice age mammoths, have been preserved in frozen soil or in the oozing tar of oil seeps. The probability that actual remains of soft tissue will be preserved is improved if the organism dies in an environment of rapid deposition and oxygen deprivation. Under such conditions, the destructive effects of bacteria are diminished. The Middle Eocene Messel Shale (from about 48 million years ago) of Germany accumulated in such an environment. The shale was deposited in an oxygen-deficient lake where lethal gases sometimes bubbled up and killed animals. Their remains accumulated on the floor of the lake and were then covered by clay and silt. Among the superbly preserved Messel fossils are insects with iridescent exoskeletons (hard outer coverings), frogs with skin and blood vessels intact, and even entire small mammals with preserved fur and soft tissue.