By measuring tiny amounts of radioactive elements in coral, scientists

Question

By measuring tiny amounts of radioactive elements in coral, scientists have recently discovered unexpectedly large errors in the traditional carbon-dating scale. Researchers say the coral experiments will not only alter the previously established dates of important prehistoric events but will also help to resolve the question of how quickly the earth warmed at the end of the last ice age.

These findings are based on a study of coral samples taken from reefs in the waters of Barbados. Researchers dated the coral using two different radioactive "clocks": the decay of carbon-14 and the decay of uranium to thorium. The latter entails the use of a mass spectrometer to measure the relative amounts of uranium and thorium isotopes in the coral. This method, now known as the thorium technique can date only a limited variety of materials and therefore can never completely replace the carbon-14 method. But the thorium dates do provide valuable calibration points that provide a clearer picture of "real" calendar ages.

The ages determined by the thorium technique suggest extreme fluctuations in the concentration of carbon-14, with the Ice Age's atmosphere holding up to 40 percent more carbon-14 than does today's. Researchers report using the thorium technique to re-calibrate the carbon-14 scale of the past 30,000 years, an advance one scientist describes as a “quantum leap." Their results suggest that the carbon-14 method occasionally has a large margin of error, producing dates of as many as 3,500 years too young for material that is in fact at least 20,000 years old. While carbon-14 specialists knew the scale needed correction, most were surprised at the magnitude of the correction that was required.    1 
 1. According to the passage, the effectiveness of the thorium technique

A. is not widely accepted in the scientific community
B. surpasses that of carbon-14 testing
C. will change the focus of scientific research
D. is limited to certain types of materials
E. lies in its ability to measure calibration points in carbon-14

2 
 2. According to the passage, the experiments conducted on coral

A. will confirm previously established dates of prehistoric events
B. will help to settle questions about the end of the last ice age
C. were conducted at a variety of sites over several years
D. have helped to replace carbon-14 testing with the thorium technique
E. were conducted in order to compare the effectiveness of two different radioactive "clocks"

3 
 3. Which of the following can be inferred from the information in the passage about improvements in carbon-14 dating techniques?

A. All dating techniques are more useful when calibrated with the thorium technique.
B. Many scientists have doubted the accuracy of the thorium technique.
C. Some events previously believed to have occurred around 16,500 years ago may have occurred around 20,000 years ago.
D. Coral samples have greater concentrations of thorium than of carbon-14.
E. Mass spectrometers can be used to measure carbon-14 as well as the ratio of uranium to thorium.

4 
 4. According to the passage, the best use of the dating method used on the Barbados coral would be

A. as a replacement for the carbon-14 method
B. as a substitute for the standard method for only those materials that do not contain carbon-14
C. as a tool to date a wider variety of materials than carbon dating can alone
D. to determine the fluctuating amounts of carbon-14 in the environment at a specific time
E. as a calibration device for the carbon-dating method

5 
 5. The passage suggests that scientists consider which of the following methods of dating prehistoric material to be the most accurate?

A. Experimenting with the new method of measuring the decay of uranium to thorium
B. Measuring carbon-14 locked within organic material from plants and animals
C. Formulating deductions from the combined use of the carbon-dating and calibration techniques
D. Comparing thorium and carbon-14 found in the organic material in which the concentration of those elements in the environment is known
E. Assessing the rate of decay of all radioactive elements within certain organic material

6 
 6. With which of the following statements concerning carbon-dating would the author most likely agree?

A. the carbon-dating method should be used in conjunction with other techniques that compensate for possible inaccuracies.
B. The carbon-dating method is extremely inaccurate and therefore obsolete.
C. With improved calibration, carbon dating can accurately date events that occurred as many as 40,000 years ago.
D. The carbon-dating method should be considered accurate for certain organic substances but less accurate for others. 
E. The carbon-dating method is most useful in measuring the age of objects less than 8,000 years old.

7 
 7. The author is primarily concerned with

A. presenting the inadequacies of one method and the reasons it should be replaced
B. describing the advantages of an established method over newer, less universally applicable methods
C. evaluating the drawbacks of a new method in comparison with other methods that have equally serious, but different disadvantages
D. identifying a weakness inherent in one method and presenting another method that could somewhat minimize the impact of this weakness
E. criticizing an established method but admitting that a suitable alternative has yet to be found

ash124 · Answer

Understand the passage and try to create a map:

Identifying an error in the existing method 
Describe a different method that can rectify the errors
The magnitude of error in C14 method

1. According to the passage, the effectiveness of the thorium technique

A. is not widely accepted in the scientific community
 Not given in the passage 
B. surpasses that of carbon-14 testing
 Not given in the passage 
C. will change the focus of scientific research
 the passage doesn't say it 
D. is limited to certain types of materials
 Given in the 2nd para. 
E. lies in its ability to measure calibration points in carbon-14
  thorium technique is not dependent on carbon-14 method

Answer D

2. According to the passage, the experiments conducted on coral

A. will confirm previously established dates of prehistoric events
 It will correct the error not confirm 
B. will help to settle questions about the end of the last ice age
 Given in the 1st para. 
C. were conducted at a variety of sites over several years
 not given in the passage 
D. have helped to replace carbon-14 testing with the thorium technique
 thorium technique is not replacing carbon-14 testing 
E. were conducted in order to compare the effectiveness of two different radioactive "clocks"
 not given in the passage

Answer C

3. Which of the following can be inferred from the information in the passage about improvements in carbon-14 dating techniques?

A. All dating techniques are more useful when calibrated with the thorium technique.
 Nothing is given about other techniques 
B. Many scientists have doubted the accuracy of the thorium technique.
 Not given 
C. Some events previously believed to have occurred around 16,500 years ago may have occurred around 20,000 years ago.
 Yes, given in the 3rd para. 
D. Coral samples have greater concentrations of thorium than of carbon-14.
no comparisons given
E. Mass spectrometers can be used to measure carbon-14 as well as the ratio of uranium to thorium.
 False statement based on 2nd para. 
 Answer C

4. According to the passage, the best use of the dating method used on the Barbados coral would be

A. as a replacement for the carbon-14 method
 Not given 
B. as a substitute for the standard method for only those materials that do not contain carbon-14
 Too narrow 
C. as a tool to date a wider variety of materials than carbon dating can alone
 thorium technique is limited to a certain matter 
D. to determine the fluctuating amounts of carbon-14 in the environment at a specific time
 Not given  
E. as a calibration device for the carbon-dating method
 yes, the Main point

Answer E

5. The passage suggests that scientists consider which of the following methods of dating prehistoric material to be the most accurate?

A. Experimenting with the new method of measuring the decay of uranium to thorium
 Not given 
B. Measuring carbon-14 locked within organic material from plants and animals
 Not given 
C. Formulating deductions from the combined use of the carbon-dating and calibration techniques
Yes, supported
D. Comparing thorium and carbon-14 found in the organic material in which the concentration of those elements in the environment is known
 Not given 
E. Assessing the rate of decay of all radioactive elements within certain organic material
 Not given

6. With which of the following statements concerning carbon-dating would the author most likely agree?

A. the carbon-dating method should be used in conjunction with other techniques that compensate for possible inaccuracies.
 Yes, the author agrees with it 
B. The carbon-dating method is extremely inaccurate and therefore obsolete.
 too extreme  
C. With improved calibration, carbon dating can accurately date events that occurred as many as 40,000 years ago.
 nowhere given 
D. The carbon-dating method should be considered accurate for certain organic substances but less accurate for others.
 nowhere given  
E. The carbon-dating method is most useful in measuring the age of objects less than 8,000 years old.
 not mentioned in the passage

Answer A

7. The author is primarily concerned with

A. presenting the inadequacies of one method and the reasons it should be replaced
 no replacement is suggested in the passage 
B. describing the advantages of an established method over newer, less universally applicable methods
 disadvantages of the established method are given  
C. evaluating the drawbacks of a new method in comparison with other methods that have equally serious, but different disadvantages
 no comparison is done 
D. identifying a weakness inherent in one method and presenting another method that could somewhat minimize the impact of this weakness
 The crux of the passage 
E. criticizing an established method but admitting that a suitable alternative has yet to be found   
 not supported 
 Answer D

c93liu · Answer

Q1 - my answer is D)

A) - Not mentioned in the passage and seems like the contrary is actually implied.
B) - We know from the passage that the technique is more limited in application setting vs. Carbon-14, so B) is out.
C) - This is rather extreme. While thorium technique may help to calibrate results obtained from Carbon-14 and hence provide more accurate results and new insights, to say that it will change the focus of scientific research seems to be too exaggerated.
D) - Yes, this is directly stated in paragraph 2: "the thorium technique can date only a limited variety of materials"
E) - The dates obtained from the thorium technique provides calibration points, not the technique itself.

Q2 - my answer is B)

A) - Seems to be the contrary of what the passage is actually discussing.
B) - Yes, see paragraph 1: "will also help to resolve the question of how quickly the earth warmed at the end of the last ice age"
C) - We know the experiments were conducted from reefs in Barbados (so potentially a variety of sites), but not sure about "over several years" - no such mentions.
D) - This is the contrary of paragraph 2 of the passage: "... and therefore can never completely replace the carbon-14 method".
E) - This is not the main objective of the experiments.

Q3 - my answer is C)

A) - This option takes the passage to an extreme. Although in these specific experiments, the thorium technique complements Carbon-14, it is rather extreme to say that all dating techniques are more useful with the technique.
B) - This option is not mentioned at all in the passage.
C) - Yes. In paragraph 3, we know that Carbon-14 can produce "dates of as many as 3,500 years too young for material that is in fact at least 20,000 years old". 20,000 - 3,500 = 16,500.
D) - We do not know the relative concentration between the 2, other than the fact that coral reefs contain both.
E) - Again, we do not know this from the passage alone.

Q4 - my answer is E)
From paragraph 2: "But the thorium dates do provide valuable calibration points that provide a clearer picture of "real" calendar ages", suggesting that the thorium technique acts as an additional calibration of Carbon-14 dates.

A) - Complements, but not replaces Carbon-14.
B) - See A).
C) - This goes exactly the opposite of paragraph 2.
D) - The fluctuating amounts of Carbon-14 in the environment is the explanation for why Carbon-14 failed to provide an accurate reading, but not the direct use / result of the thorium technique.
E) - Yes, this matches with our thinking above.

Q5 - my answer is C)
Should be the combination of Carbon-14 with some calibration technique.

A) - Notice that we are talking about prehistoric materials generally. We know that the thorium technique has more limited application sets, so A) is out.
B) - The passage's discussion about coral reefs clearly provides one counter-example to this.
C) - Yes, this matches with our thinking above.
D) - Again, see A). Too narrow vs. the broadly discussed term prehistoric material.
E) - The passage only mentions two specific types of decay "clocks". Not sure about all radioactive decays.

Q6 - my answer is A)

A) - Yes, Carbon-14 + the thorium technique as discussed in the passage.
B) - Taking the passage to an extreme. Carbon-14 is more like the backbone.
C) - We do not know about the effective range of Carbon-14. This is not discussed in the passage.
D) - Also not discussed in the passage.
E) - See C) above.

Q7 - my answer is D)

A) - Inadequacies of Carbon-14, maybe, replacement of Carbon-14, no way.
B) - If this were true, we would be talking about how much better Carbon-14 is over the thorium technique. Not true.
C) - The passage talks about how Carbon-14 + thorium > Carbon-14 alone, not comparing the drawback of Carbon-14 vs. thorium.
D) - Yes. The weakness in Carbon-14 is from the fluctuating amount of Carbon-14 in the environment. Another method to mitigate this drawback is Carbon-14 + calibration technique (thorium).
E) - Not true. A suitable alternative is Carbon-14 + calibration technique.

Gaudapada · Answer

1. According to the passage, the effectiveness of the thorium technique

A. is not widely accepted in the scientific community  
This is never mentioned in the passage. The only drawback of the thorium technique stated by the author is the limited variety of materials that it can date.

B. surpasses that of carbon-14 testing  
Thorium technique is not mentioned to be superior to carbon-14 technique. "The thorium dates do provide valuable calibration points that provide a clearer picture of "real" calendar ages", but author never states that it is superior by itself.

C. will change the focus of scientific research  
This could be true of the Barbados study but author never directly mentions that the thorium technique by itself is revolutionary.

D. is limited to certain types of materials  
 CORRECT :  This is directly stated in  paragraph 2 
 "This method, now known as the thorium technique can date only a limited variety of materials and therefore can never completely replace the carbon-14 method"

E. lies in its ability to measure calibration points in carbon-14  
The thorium technique is not dependent on the carbon technique. When used in conjunction with carbon-14 this is true but the use of thorium technique as a calibration for the carbon-14 technique has no relevance to the thorium technique's own effectiveness.

2. According to the passage, the experiments conducted on coral

A. will confirm previously established dates of prehistoric events  
The experiments achieved the opposite effect, altering previously established dates of prehistoric events.

B. will help to settle questions about the end of the last ice age  
 CORRECT :  This is mentioned explicitly in  paragraph 1 
 "Researchers say the coral experiments will not only alter the previously established dates of important prehistoric events but will also help to resolve the question of how quickly the earth warmed at the end of the last ice age."

C. were conducted at a variety of sites over several years  
from  paragraph 2 , the experiments were conducted only on the Barbados site. Hence  variety of sites  is incorrect.

D. have helped to replace carbon-14 testing with the thorium technique  
From  paragraph 3 , The thorium technique is used as calibration for the carbbon-14 scale. Hence carbon-14 has not been  replaced

E. were conducted in order to compare the effectiveness of two different radioactive "clocks"  
While two different clocks were used, This was not the purpose of the experiment. Answer choice  E  conflates methodology with result.

3. Which of the following can be inferred from the information in the passage about improvements in carbon-14 dating techniques?

A. All dating techniques are more useful when calibrated with the thorium technique.  
While the passage says that carbon-14 technique is more useful when calibrated with thorium technique, it would be a generalization to assume the same for  ALL  dating techniques.

B. Many scientists have doubted the accuracy of the thorium technique.  
This is never mentioned in the passage. The drawback of thorium technique (limited to certain materials) is mentioned but this does not mean that scientists doubt the accuracy of thorium technique as a whole.

C. Some events previously believed to have occurred around 16,500 years ago may have occurred around 20,000 years ago.  
 CORRECT :  The dates in  paragraph 3  are mentioned in an approximate way. Since no other option is favorable,  C  must be correct.

D. Coral samples have greater concentrations of thorium than of carbon-14.  
Relative concentrations of thorium and carbon-14 in coral samples is not mentioned in the passage.

E. Mass spectrometers can be used to measure carbon-14 as well as the ratio of uranium to thorium.  
from  paragraph 2 ,  "Researchers dated the coral using two different radioactive "clocks": the decay of carbon-14 and the decay of uranium to thorium. The latter entails the use of a mass spectrometer to measure the relative amounts of uranium and thorium isotopes in the coral. This method" 
the latter method(thorium) is mentioned to use mass spectrometers but nothing is said about the carbon-14 technique in this regard.

4. According to the passage, the best use of the dating method used on the Barbados coral would be

A. as a replacement for the carbon-14 method  
Thorium technique is not a  REPLACEMENT  for the carbon-14 method.

B. as a substitute for the standard method for only those materials that do not contain carbon-14  
While this may be a use for thorium dating, it is not mentioned by the  AUTHOR

C. as a tool to date a wider variety of materials than carbon dating can alone  
The main crux of the passage is that the thorium technique, when used as a calibration for the carbon-14 scale provide provide more accurate dates for established prehistoric events. The dating of materials is not the focus of the passage, the dating of prehistoric events is.

D. to determine the fluctuating amounts of carbon-14 in the environment at a specific time  
from  paragraph 3 ,  "The ages determined by the thorium technique suggest extreme fluctuations in the concentration of carbon-14, with the Ice Age's atmosphere holding up to 40 percent more carbon-14 than does today's" 
The extreme fluctuations is carbon-14 caused the inaccuracy of dates. Thorium techniques suggest extreme fluctuations but nowhere is it mentioned that the amount of fluctuation can be determined.

E. as a calibration device for the carbon-dating method  
 CORRECT :  This is directly mentioned in  paragraph 3 .  "But the thorium dates do provide valuable calibration points that provide a clearer picture of "real" calendar ages."

5. The passage suggests that scientists consider which of the following methods of dating prehistoric material to be the most accurate?

A. Experimenting with the new method of measuring the decay of uranium to thorium  
The new method(thorium) by itself is not mentioned as the most accurate in this passage.

B. Measuring carbon-14 locked within organic material from plants and animals  
the distinction between organic and inorganic material is never made in the passage. We can quickly dismiss this answer.

C. Formulating deductions from the combined use of the carbon-dating and calibration techniques  
 CORRECT :  This is the crux of  paragraph 3 
 ""Researchers report using the thorium technique to re-calibrate the carbon-14 scale of the past 30,000 years, an advance one scientist describes as a “quantum leap."

D. Comparing thorium and carbon-14 found in the organic material in which the concentration of those elements in the environment is known  
Comparison of thorium and carbon-14 sounds suspicious. Author mentions recalibration of carbon-14 scale with thorium method, not a comparison between the two. Furthermore, thorium concentration in the environment is never mentioned in the passage.

E. Assessing the rate of decay of all radioactive elements within certain organic material  
Passage never mentions any method involving rate of decay of  ALL  radioactive elements.

6. With which of the following statements concerning carbon-dating would the author most likely agree?

A. the carbon-dating method should be used in conjunction with other techniques that compensate for possible inaccuracies.  
 CORRECT :  Author never dismisses the carbon-14 technique. It can be used in conjunction with other techniques(like thorium technique) to yield accurate dates.

B. The carbon-dating method is extremely inaccurate and therefore obsolete.  
This is directly contradicted in  paragraph 3 . While the technique can be inaccurate by itself, it can still be used in conjunction with other techniques.

C. With improved calibration, carbon dating can accurately date events that occurred as many as 40,000 years ago.  
The specific mention of  as many as 40,000 years ago  is suspicious. No such date is mentioned or can be inferred from the passage.

D. The carbon-dating method should be considered accurate for certain organic substances but less accurate for others.  
The accuracy of carbon dating method is never mentioned to be a function of the material being tested. No mention of organic matter is ever made in the passage.

E. The carbon-dating method is most useful in measuring the age of objects less than 8,000 years old.  
Passage never suggests that the carbon-dating method is more accurate for objects younger than 8000 years or that it is inaccurate for objects older than 8000 years old. This date is neither mentioned nor can it be inferred.

7. The author is primarily concerned with

A. presenting the inadequacies of one method and the reasons it should be replaced  
Author never advocates for a  REPLACEMENT  of the carbon-14 technique.

B. describing the advantages of an established method over newer, less universally applicable methods  
Author mentions the disadvantage of the  ESTABLISHED  method (carbon-14) so this option cannot be true.

C. evaluating the drawbacks of a new method in comparison with other methods that have equally serious, but different disadvantages  
This misses the point of the passage. The primary concern of the author is to describe the significance of the Barbados experiment, and how thorium technique in conjunction with carbon-14 is a " quantum leap " in dating techniques.

D. identifying a weakness inherent in one method and presenting another method that could somewhat minimize the impact of this weakness  
 CORRECT :  This answer best fits the primary concern of the author. A weakness in carbon-14 method is identified, and another method(thorium) is presented which could minimize the impact of the weakness.

E. criticizing an established method but admitting that a suitable alternative has yet to be found  
This option is incorrect because a suitable option is described. ( a conjunction of the two techniques).

irisjojojo · Answer

Question 1: D "This method, now known as the thorium technique can date only a limited variety of materials and therefore can never completely replace the carbon-14 method. But the thorium dates do provide valuable calibration points that provide a clearer picture of "real" calendar ages." Question 2: B A --> "confirm" is wrong here. The coral experiments is used to correct ("alter") the previous established erroneous date C --> "at a variety of sites over several years" --> not mentioned D --> the passage never says carbon-14 testing can be replaced (in fact, it suggests the other way around. ) E --> nope, the purpose is not for comparison Question 3: C A --> " All dating techniques are more useful" --> nope B --> "Many scientists have doubted" --> nope nope, "doubt" is never mentioned in the paragraph D --> have greater concentrations --> no evidence E --> not sure where the passage mentions "mass spectrometer" Question 4: E A --> can not substitute because... "can date only a limited variety of materials and therefore can never completely replace the carbon-14 method" B --> the concept of " only " (limitation) is not mentioned in the passage C --> true, but not the best use of the method C --> "at a specific time" --> not true E is better than D because the author indicates in the last sentence: "While carbon-14 specialists knew the scale needed correction, most were surprised at the magnitude of the correction that was required." Thus, we can conclude that thorium technique is used to calibrate and serves as a supplement of the carbon-dating method. Question 5: C D --> knowing the concentration of elements is not needed From the experience of the previous question, we can deduct that the answer should be C, the combination of the two methods. Question 6: A B --> obsolete? --> of course not C --> "as many as 40,000 years ago" suggests that the accuracy is limited to 40,000 years ago, but that is not the case D --> not mentioned; "less accurate for others (substances)" --> not justified E --> not mentioned; "most useful" --> not justified A --> compatible with the passage (discussed multiple times in previous question.) Question 7: D A --> stated many times, NOT replaced B --> the passage is NOT describing the "advantages" of carbon-dating method! C --> "evaluating the drawbacks of a new method" totally wrong. Thorium technique may have limitation, but the author is definitely not focusing on its disadvantages. E --> "has yet to be found" --> nope --> suitable alternative is not perfect, but is discovered. Finally done, mission complete

By measuring tiny amounts of radioactive elements in coral, scientists

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By measuring tiny amounts of radioactive elements in coral, scientists

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