『週刊ST』7/23「TOEFL® iBT対策講座」問題

Fossils

1. Fossils are the remains and traces of past life or any other direct evidence of past life. Traces include trails, footprints, burrows, worm casts, or even preserved droppings. Usually when an organism dies, the soft parts are either consumed by scavengers or undergo bacterial decomposition. Occasionally, the organism is buried quickly and in such a way that decomposition is never completed or is completed so slowly that the soft parts leave an imprint of their structure. Most fossils, however, consist only of hard parts such as shells, bones or teeth, because these are usually not consumed or destroyed.
2. The great majority of fossils are found embedded in or recently eroded from sedimentary rock. Sedimentation, a process that has been going on since the earth was formed, can take place on land or in bodies of water. Weathering and erosion of rocks produces an accumulation of particles that vary in size and nature and are called sediment. Sediment becomes a stratum (plural, strata), a recognizable layer in a stratigraphic sequence. Any given stratum is older than the one above it and younger than the one immediately below it.
3. The fossils trapped in strata are the fossil record that tells us about the history of life. Palaeontology is the science of discovering and studying the fossil record and, from it, making decisions about the history of life. Palaeontologists not only want to know the structure and adaptations of an organism, they are also interested in how the organism interacted with others and with the physical environment.
4. In the early nineteenth century, even before the theory of evolution was formulated, geologists sought to [correlate] the strata worldwide. The problem was that strata change their character over great distances, and therefore a stratum in England might contain different sediments than one of the same age in Russia. Geologists discovered, however, that a stratum of the same age tend to contain the same fossil, and therefore, fossils could be used for the purpose of relative dating of the strata. For example, a particular species of fossil ammonite (an animal related to the chambered nautilus) has been found over a wide range and for a limited time period. Therefore, all strata around the world that contain this fossil must be of the same age .
5. This approach helped geologists determine the relative dates of the strata despite upheavals, but it was not particularly helpful to biologists who wanted to know the absolute age of fossils in years.
6. The absolute dating method that relies on radioactive dating techniques assigns an actual date to a fossil. All radioactive isotopes have a particular half-life, the length of time it takes for half of the radioactive isotope to change into another stable element. If the fossil has organic matter, half of the carbon-14, 14C, will have changed to nitrogen-14, 14N, in 5,730 years. [A] In order to know how much 14C was in the organism to begin with, it is reasoned that organic matter always begins with the same amount of 14C. [B] (In reality, it is known that the 14C levels in the air — and therefore the amount in organisms — can vary from time to time.) [C] Now we need only compare the 14C radioactivity of the fossil to that of a modern sample of organic matter. The amount of radiation left can be converted to the age of the fossil. [D]
7. 14C is the only radioactive isotope contained within organic matter, but it is possible to use others to date rocks and from that infer the age of a fossil contained in the rock. For instance, the ratio of potassium-40 (40K) to argon-40 trapped in rock is often used. If the ratio is 1:1, then half of the 40K has decayed and the rock is 1.3 billion years old. The ratio of isotope uranium-238 to lead-207 can be used only for rocks older than 100 million years. This isotope has such a long half-life that no perceptible decay will have occurred in a shorter length of time.

1. According to the passage, a fossil is
   
   
   
   1. anything that tells us about past life.
   
   
   2. the hard parts of an animal.
   
   
   3. an animal that was buried quickly.
   
   
   4. another word for a trace.


2. It is stated in the passage that
   
   
   
   1. strata are formed by sedimentation.
   
   
   2. strata are formed by volcanic activity.
   
   
   3. newer strata are found below older ones.
   
   
   4. all fossils are found in sedimentary rock.


3. The problem nineteenth century geologists had was that
   
   
   
   1. different fossils are found in different countries.
   
   
   2. different rocks are found in different countries.
   
   
   3. different strata are found in different countries.
   
   
   4. strata in some countries are older than in others..


4. It can be inferred from the passage that
   
   
   1. the theory of evolution was formulated after 1800.
   
   
   2. fossils were not discovered until the nineteenth century.
   
   
   3. palaeontology is younger than the theory of evolution.
   
   
   4. geology began in the nineteenth century.


5. Which of the following is NOT mentioned in the passage?
   
   
   1. The age of a stratum can be deduced from the fossils it contains.
   
   
   2. The fossil ammonite can be found in different parts of the world.
   
   
   3. Strata have different characteristics in different parts of the world.
   
   
   4. The study of strata is known as stratigraphy


6. Look at the word correlate in paragraph 4. This word could best be replaced by
   
   
   1. study
   
   
   2. match
   
   
   3. date
   
   
   4. analyze


7. Look at the word relativein paragraph 5. This word could best be replaced by
   
   
   
   1. exact
   
   
   2. approximate
   
   
   3. comparative
   
   
   4. actual


8. What is radioactive dating used for?
   
   
   
   1. To establish the absolute age of a fossil.
   
   
   2. To establish which strata are older than others.
   
   
   3. To determine what kind of rock a fossil is found in.
   
   
   4. To determine what kind of matter a fossil contains.


9. The following sentence can be added to the passage. “After 50,000 years, however, the amount of 14C radioactivity is so low it cannot be used to measure the age of a fossil accurately.”Where would it best fit?
   
   
   
   1. A
   
   
   2. B
   
   
   3. C
   
   
   4. D


10. What disadvantage of uranium-238 is mentioned?
    
    
    
    1. It is only found in rocks over 100 million years old.
    
    
    2. It cannot be used to date recent rocks.
    
    
    3. Very few rocks contain it.
    
    
    4. It is difficult to date rocks accurately using it.


11. What is the main topic of this passage?<
    
    
    
    1. The history of Palaeontology.
    
    
    2. How we can learn from fossils.
    
    
    3. The differences between types of rock.
    
    
    4. How radioactivity can be used to date rocks.


12. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices (by numbering the boxes) 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.

    Fossils are the record of the development of life on earth.
    

    Answer Choices

    □　It is possible to know the relative ages of fossils from the strata they are found in.

    □　Many fossils are preserved in museums.

    □　However to find their absolute age, it is necessary to use radioactive dating.

    □　Ammonite fossils can be found in many parts of the world.

    □　Most fossils are found in layers of sedimentary rock known as strata.

    □　Fossils can include traces such as footprints.
    

    Number the boxes according to where the answer choices belong in the summary.
    

『週刊ST』7/23「TOEFL® iBT対策講座」解説

今回取り上げる自然科学系のパッセ-ジは、日本人の多くが苦手としています。これは、私たちが自然科学の英文を読む機会が少ないからです。TOEFL○Rを受験する人は、物理、科学、生物、数学などのアメリカの高等学校課程の教科書などは一通り目を通しておいた方がよいでしょう。

設問1: 正解（A）
設問2: 正解 (A)

第二パラグラフ三行目から六行目にかけて、「土石の風化や侵食といった活動が堆積物(sediment)を蓄積させる。この堆積物が地層(a stratum)となる。」という内容が述べられています。この部分が論拠となり、正解(A)が導かれます。

設問3: 正解 (B)
設問4: 正解 (A)

第四パラグラフ冒頭で、「十九世紀初頭、すなわち進化論が形成される以前から、地質学者たちは全世界的に多くの地層を関連付けるべく努力していた。」と述べられています。この部分から、正解(A)が導かれます。進化論がダーウィンによって提唱されたのは１９世紀後半であることは、ある意味常識ですが、TOEFL○Rでは、本文で述べられていない論拠を常識によって補わなければならないような問題は出ません。

設問5: 正解 (D)
設問6: 正解 (B)
設問7: 正解 (C)

TOEFL○Rの語彙問題としてはもっとも基本的なレベルです。このような問題では絶対に失点しないようにして下さい。

設問8: 正解 (A)
設問9: 正解 (D)
設問10: 正解 (B)

第七パラグラフ五行目から六行目の文で、「同位元素 uranium-238 と lead-207の比率は、一億年以上前の rock (化石も含む)に関してのみ用いられる。」とあります。従って、正解は(B)となります。

設問11: 正解 (B)
設問12: 正解 (E)→(A)→(C)

(B)は、一見常識にかなっているように見えます。しかし、本文のどこにも触れられていません。(D)と(F)はともに本文中に述べられてはいますが、瑣末な情報ですので要約の一部とは成り得ません。