To study centuries-old earthquakes and the geologic faults that caused

Question

To study centuries-old earthquakes and the geologic faults that caused them, seismologists usually dig trenches along visible fault lines, looking for sediments that show evidence of having shifted. Using radiocarbon dating, they measure the quantity of the radioactive isotope carbon 14 present in wood or other organic material trapped in the sediments when they shifted. Since carbon 14 occurs naturally in organic materials and decays at a constant rate, the age of organic materials can be reconstructed from the amount of the isotope remaining in them. These data can show the location and frequency of past earthquakes and provide hints about the likelihood and location of future earthquakes.

Geologists William Bull and Mark Brandon have recently developed a new method, called lichenometry, for detecting and dating past earthquakes. Bull and Brandon developed the method based on the fact that large earthquakes generate numerous simultaneous rockfalls in mountain ranges that are sensitive to seismic shaking. Instead of dating fault-line sediments, lichenometry involves measuring the size of lichens growing on the rocks exposed by these rockfalls. Lichens—symbiotic organisms consisting of a fungus and an alga—quickly colonize newly exposed rock surfaces in the wake of rockfalls,  and once established they grow radially, flat against the rocks, at a slow but constant rate for as long as 1,000 years if left undisturbed.  One species of North American lichen, for example, spreads outward by about 9.5 millimeters each century. Hence, the diameter of the largest lichen on a boulder provides direct evidence of when the boulder was dislodged and repositioned. If many rockfalls over a large geographic area occurred simultaneously, that pattern would imply that there had been a strong earthquake. The location of the earthquake’s epicenter can then be determined by mapping these rockfalls, since they decrease in abundance as the distance from the epicenter increases.

Lichenometry has distinct advantages over radiocarbon dating. Radiocarbon dating is accurate only to within plus or minus 40 years, because the amount of the carbon 14 isotope varies naturally in the environment depending on the intensity of the radiation striking Earth’s upper atmosphere. Additionally, this intensity has fluctuated greatly during the past 300 years, causing many radiocarbon datings of events during this period to be of little value. Lichenometry,  Bull and Brandon claim, can accurately date an earthquake to within ten years. They note, however, that using lichenometry requires careful site selection and accurate calibration of lichen growth rates, adding that the method is best used for earthquakes that occurred within the last 500 years. Sites must be selected to minimize the influence of snow avalanches and other disturbances that would affect normal lichen growth, and conditions like shade and wind that promote faster lichen growth must be factored in.    1 
 1. Which one of the following most accurately expresses the main idea of the passage?

(A) Lichenometry is a new method for dating past earthquakes that has advantages over radiocarbon dating.
(B) Despite its limitations, lichenometry has been proven to be more accurate than any other method of discerning the dates of past earthquakes.
(C) Most seismologists today have rejected radiocarbon dating and are embracing lichenometry as the most reliable method for studying past earthquakes.
(D) Two geologists have revolutionized the study of past earthquakes by developing lichenometry, an easily applied method of earthquake detection and dating.
(E) Radiocarbon dating, an unreliable test used in dating past earthquakes, can finally be abandoned now that lichenometry has been developed.

2 
 2. The passage provides information that most helps to answer which one of the following questions?

(A) How do scientists measure lichen growth rates under the varying conditions that lichens may encounter?
(B) How do scientists determine the intensity of the radiation striking Earth’s upper atmosphere?
(C) What are some of the conditions that encourage lichens to grow at a more rapid rate than usual?
(D) What is the approximate date of the earliest earthquake that lichenometry has been used to identify?
(E) What are some applications of the techniques involved in radiocarbon dating other than their use in studying past earthquakes?

3 
 3. What is the author’s primary purpose in referring to the rate of growth of a North American lichen species ( Highlighted )?

(A) to emphasize the rapidity with which lichen colonies can establish themselves on newly exposed rock surfaces
(B) to offer an example of a lichen species with one of the slowest known rates of growth
(C) to present additional evidence supporting the claim that environmental conditions can alter lichens’ rate of growth
(D) to explain why lichenometry works best for dating earthquakes that occurred in the last 500 years
(E) to provide a sense of the sort of timescale on which lichen growth occurs

4 
 4. Which one of the following statements is most strongly supported by the passage?

(A) Lichenometry is less accurate than radiocarbon dating in predicting the likelihood and location of future earthquakes.
(B) Radiocarbon dating is unlikely to be helpful in dating past earthquakes that have no identifiable fault lines associated with them.
(C) Radiocarbon dating and lichenometry are currently the only viable methods of detecting and dating past earthquakes.
(D) Radiocarbon dating is more accurate than lichenometry in dating earthquakes that occurred approximately 400 years ago.
(E) The usefulness of lichenometry for dating earthquakes is limited to geographic regions where factors that disturb or accelerate lichen growth generally do not occur.

5 
 5. The primary purpose of the first paragraph in relation to the rest of the passage is to describe

(A) a well-known procedure that will then be examined on a step-by-step basis
(B) an established procedure to which a new procedure will then be compared
(C) an outdated procedure that will then be shown to be nonetheless useful in some situations
(D) a traditional procedure that will then be contrasted with other traditional procedures
(E) a popular procedure that will then be shown to have resulted in erroneous conclusions about a phenomenon

6 
 6. It can be inferred that the statements made by Bull and Brandon and reported ( Text in red at the end of the passage ) rely on which one of the following assumptions?

(A) While lichenometry is less accurate when it is used to date earthquakes that occurred more than 500 years ago, it is still more accurate than other methods for dating such earthquakes.
(B) There is no reliable method for determining the intensity of the radiation now hitting Earth’s upper atmosphere.
(C) Lichens are able to grow only on the types of rocks that are common in mountainous regions.
(D) The mountain ranges that produce the kinds of rockfalls studied in lichenometry are also subject to more frequent snowfalls and avalanches than other mountain ranges are.
(E) The extent to which conditions like shade and wind have affected the growth of existing lichen colonies can be determined.

7 
 7. The passage indicates that using radiocarbon dating to date past earthquakes may be unreliable due to

(A) the multiplicity of the types of organic matter that require analysis
(B) the variable amount of organic materials caught in shifted sediments
(C) the fact that fault lines related to past earthquakes are not always visible
(D) the fluctuations in the amount of the carbon 14 isotope in the environment over time
(E) the possibility that radiation has not always struck the upper atmosphere

8 
 8. Given the information in the passage, to which one of the following would lichenometry likely be most applicable?

(A) identifying the number of times a particular river has flooded in the past 1,000 years
(B) identifying the age of a fossilized skeleton of a mammal that lived many thousands of years ago
(C) identifying the age of an ancient beach now underwater approximately 30 kilometers off the present shore
(D) identifying the rate, in kilometers per century, at which a glacier has been receding up a mountain valley
(E) identifying local trends in annual rainfall rates in a particular valley over the past five centuries

generis · Accepted Answer

Hi ShankSouljaBoi and vp680 , here is the solution to Question 4. "Most strongly supported" questions are often among LSAC's hardest questions. In Reading Comp (and all Verbal sections), if you cannot eliminate it immediately, keep it and move on. No. The passage says nothing about lichenometry and accuracy of prediction, so we cannot compare. One sentence describes radiocarbon dating and prediction: These data can show the location and frequency of past earthquakes and provide hints about the likelihood and location of future earthquakes. No other information about prediction exists. The one mention we have is tied only to radiocarbon dating. Do not go further. Eliminate A If this is NOT the answer, I will be shocked. Passage says: To study centuries-old earthquakes ... seismologists usually dig trenches along visible fault lines , looking for sediments that show evidence of having shifted. Using radiocarbon dating . . . "Identifiable" fault lines = "visible" fault lines. The radiocarbon dating seismologists cannot dig a trench along a fault line they cannot see. KEEP (and if you are worried about what "usually" means, keep B anyway -- this option is definitely not wrong, although another answer may be better) No. The passage says nothing about any other methods. We have no idea whether any others exist. Do not be tempted by "usually" in P1 and then "a new way" in the first sentence of P2. Go back to the text. It says nothing one way or the other about other viable methods. Eliminate C. No. The "opposite answer." From the passage, P3: Lichenometry is " best used for earthquakes that occurred within the last 500 years. " " Radiocarbon dating is accurate only to within plus or minus 40 years . . . lechenometry . . . can accurately date an earthquake to within 10 years. (D) has the situation exactly backwards. As long as the earthquake happened within the last 500 years, the accuracy rate of lichenometry is ± 10 years. The accuracy rate of radiocarbon dating is ± 40 years. Lichenometry is more accurate. Eliminate D. Ah. The other at-least-somewhat correct answer. From the passage: . . . using lichenometry requires careful site selection and accurate calibration of lichen growth rates . . . Sites must be selected to minimize the influence of snow avalanches and other disturbances that would affect normal lichen growth, and conditions like shade and wind that promote faster lichen growth must be factored in Be careful with strong phrases such as "the only viable" (option C) and "i s limited to " in option E. No. Too strong. The passage contradicts the second part of (E), namely "or accelerate lichen growth." Lichenometry can be useful in regions where growth accelerators such as wind and shade are present. The conditions must simply be factored in. In other words, the passage tacitly contradicts the second part of (E). When half of the option is wrong, you can eliminate the whole question. Be done.

The first part of (E) and all of (B) may be equal in passage support. We do not know and we do not care. Half of (E) is wrong. Ciao, option E. The answer is B Hope that helps

generis · Answer

Hi ShankSouljaBoi and vp680 , here is the solution to question #8. This information from the passage is important: Lichens . . . quickly colonize newly exposed rock surfaces in the wake of rockfalls, and once established they grow at a slow but constant rate. Licihenometry is about dating things (earthquakes and lichen growth), not about measuring frequency. No mention of flooding and effect on lichen growth. Eliminate A Lichenometry is for dating earthquakes using growth rates of lichen. No mention that lichenometry can date anything else. No mention of lichen on fossils. Eliminate B. Lichenometry relies on lichen that grows on exposed surfaces, not underwater.

Eliminate C Probably correct. Melting ice glaciers expose mountain rock on which lichen can grow. Lichen grow on exposed rocks. The larger the circle of lichen, the longer the rock has been exposed (by the melting glacier). Probably correct. KEEP No. Don't be tempted by "past five centuries." Rainfall? Options A and C were bad—(E) is worse. Lichenometry does not measure trends in rainfall. Eliminate E. The answer is D. Hope that helps.

ShankSouljaBoi · Answer

Kindly provide official explanation for q4 and q8

vp680 · Answer

kindly help with 4th and 8th

hero_with_1000_faces · Answer

In Question No. 4,

(E) The usefulness of lichenometry for dating earthquakes is limited to geographic regions where factors that disturb or accelerate lichen growth generally do not occur.

E is incorrect, as the passage states "that the factors accelerating growth must be taken into consideration".
If the passage would have stated that " there shall not be any elements that accelerate or affect the growth of Linchen" then E would have been right answer.

Hence, Linchen remains useful even if such factors exist, E can be eliminated.

MikeScarn · Answer

Explanation for #6 Question Type: Inference and Assumption Do we know this for sure? This answer choice attempts to bait us into assuming that Lichenometry is more accurate than other methods. The only other method that is discussed is radio carbon dating. We have no knowledge of what other methods may be out there. This answer choice is a completely unwarranted assumption. Further, Ball and Brandon's statements certainly do not " rely " on this faulty assumption. Eliminate This assumption is completely irrelevant. Nowhere do Ball and Brandon's statements discuss radiation hitting the Earth's upper atmosphere. Radio carbon dating, the other method, is related to measuring radiation hitting the Earth's upper atmosphere. If you chose this answer, you probably didn't look back at the red text and understand what the question is asking. Eliminate This answer choice is equally as irrelevant as (B). In no way can we infer that (C) is an assumption that Ball and Brandon's statements rely on. Eliminate This answer choice is also out of left-field. The red text does say that careful site selection is a limitation of lichenometry, and that one of the factors in site selection is to avoid areas where avalanches or other disturbances may have happened, as those occurrences could effect the lichen growth rate. However, we do not know that rockfalls studied in lichenometry are subject to more snowfalls and avalanches than other mountain ranges. Completely out of scope. Eliminate The red text tells us that " conditions like shade and wind that promote faster lichen growth must be factored in " when performing lichenometry. Well, if shade and wind must be factored in, then that means that we can measure the extent to which they affect the growth rate. To make it simpler, what if we used the negation method on this assumption? Negation method: If the extent to which shade and wind affect the growth rate can not be determined, then how could we factor in conditions like shade and wind? The negated version of this answer choice completely wrecks the last sentence of the passage. We have our answer

MikeScarn · Answer

#2 is clearly answered by looking at the last sentence of the entire passage. Last sentence of the passage: (C) What are some of the conditions that encourage lichens to grow at a more rapid rate than usual? Shade and wind

Harsh2111s · Answer

VeritasKarishma   GMATNinja ,
8. Given the information in the passage, to which one of the following would lichenometry likely be most applicable?
 
How above option is wrong ?
We do not know whether lichenometry will help identifying local trends or not.
May be its possible we can get trends of rainfall by growth rate of lichens.

Someone just mentioned "Lichenometry does not measure trends in rainfall"
Its just an assumption, we don't know that.
Please explain, why E can't be correct and only D can be correct ?

KarishmaB · Answer

You have to look for what is supported by the passage. The one for which you have no info in the passage is automatically out.

The passage clearly says:
Lichens quickly colonize newly exposed rock surfaces... and once established they grow radially, flat against the rocks, at a slow but constant rate for as long as 1,000 years if left undisturbed.

So when glacier will recede up a mountain valley, rock surface will be exposed. Lichens will colonise and grow at a constant rate.

Nothing is mentioned about rainfall and how it affects lichen growth.

CEdward · Answer

1. Which one of the following most accurately expresses the main idea of the passage?

(A) Lichenometry is a new method for dating past earthquakes that has advantages over radiocarbon dating. CORRECT
(B) Despite its limitations, lichenometry has been proven to be more accurate than any other method of discerning the dates of past earthquakes. X
(C) Most seismologists today have rejected radiocarbon dating and are embracing lichenometry as the most reliable method for studying past earthquakes. X
(D) Two geologists have revolutionized the study of past earthquakes by developing lichenometry, an easily applied method of earthquake detection and dating. X
(E) Radiocarbon dating, an unreliable test used in dating past earthquakes, can finally be abandoned now that lichenometry has been developed. X

2. The passage provides information that most helps to answer which one of the following questions?

(A) How do scientists measure lichen growth rates under the varying conditions that lichens may encounter? X
(B) How do scientists determine the intensity of the radiation striking Earth’s upper atmosphere? X
(C) What are some of the conditions that encourage lichens to grow at a more rapid rate than usual? CORRECT
(D) What is the approximate date of the earliest earthquake that lichenometry has been used to identify? X
(E) What are some applications of the techniques involved in radiocarbon dating other than their use in studying past earthquakes? X

3. What is the author’s primary purpose in referring to the rate of growth of a North American lichen species (Highlighted)?

(A) to emphasize the rapidity with which lichen colonies can establish themselves on newly exposed rock surfaces X
(B) to offer an example of a lichen species with one of the slowest known rates of growth X
(C) to present additional evidence supporting the claim that environmental conditions can alter lichens’ rate of growth X
(D) to explain why lichenometry works best for dating earthquakes that occurred in the last 500 years X
(E) to provide a sense of the sort of timescale on which lichen growth occurs CORRECT

4. Which one of the following statements is most strongly supported by the passage?

(A) Lichenometry is less accurate than radiocarbon dating in predicting the likelihood and location of future earthquakes. X
(B) Radiocarbon dating is unlikely to be helpful in dating past earthquakes that have no identifiable fault lines associated with them. X
(C) Radiocarbon dating and lichenometry are currently the only viable methods of detecting and dating past earthquakes.X
(D) Radiocarbon dating is more accurate than lichenometry in dating earthquakes that occurred approximately 400 years ago. X
(E) The usefulness of lichenometry for dating earthquakes is limited to geographic regions where factors that disturb or accelerate lichen growth generally do not occur. CORRECT (Correct answer is B)

5. The primary purpose of the first paragraph in relation to the rest of the passage is to describe

(A) a well-known procedure that will then be examined on a step-by-step basis X
(B) an established procedure to which a new procedure will then be compared CORRECT
(C) an outdated procedure that will then be shown to be nonetheless useful in some situations
(D) a traditional procedure that will then be contrasted with other traditional procedures X
(E) a popular procedure that will then be shown to have resulted in erroneous conclusions about a phenomenon X

6. It can be inferred that the statements made by Bull and Brandon and reported (Text in red at the end of the passage) rely on which one of the following assumptions?

(A) While lichenometry is less accurate when it is used to date earthquakes that occurred more than 500 years ago, it is still more accurate than other methods for dating such earthquakes. X
(B) There is no reliable method for determining the intensity of the radiation now hitting Earth’s upper atmosphere. X
(C) Lichens are able to grow only on the types of rocks that are common in mountainous regions. X
(D) The mountain ranges that produce the kinds of rockfalls studied in lichenometry are also subject to more frequent snowfalls and avalanches than other mountain ranges are. X
(E) The extent to which conditions like shade and wind have affected the growth of existing lichen colonies can be determined. CORRECT

7. The passage indicates that using radiocarbon dating to date past earthquakes may be unreliable due to

(A) the multiplicity of the types of organic matter that require analysis X
(B) the variable amount of organic materials caught in shifted sediments X
(C) the fact that fault lines related to past earthquakes are not always visible X
(D) the fluctuations in the amount of the carbon 14 isotope in the environment over time CORRECT
(E) the possibility that radiation has not always struck the upper atmosphere X

8. Given the information in the passage, to which one of the following would lichenometry likely be most applicable?

(A) identifying the number of times a particular river has flooded in the past 1,000 years X
(B) identifying the age of a fossilized skeleton of a mammal that lived many thousands of years ago X 
(C) identifying the age of an ancient beach now underwater approximately 30 kilometers off the present shore X
(D) identifying the rate, in kilometers per century, at which a glacier has been receding up a mountain valley CORRECT
(E) identifying local trends in annual rainfall rates in a particular valley over the past five centuries X

Apoorva0406 · Answer

For 2nd question even A answers the question

Sajjad1994 · Answer

Hi Apoorva0406

A  is not answered in the passage. Read the answer option  (A) .

A)   How   do scientists measure lichen growth rates under the varying conditions that lichens may encounter?

The passage does not explain the   method or process   of measuring growth rates under different conditions. It only says that calibration is needed and that certain conditions affect growth but it doesn’t describe   how scientists actually measure those rates  . So the  “How”  part is unanswered.

alpanajain · Answer

please provide explanation for 6th and 8th

Sajjad1994 · Answer

Hello alpanajain

Welcome to GMAT Club!

6. It can be inferred that the statements made by Bull and Brandon and reported (Text in red at the end of the passage) rely on which one of the following assumptions?

Explanation

The question asks you to determine an assumption underlying the statements made by Brandon and Bull in the final paragraph. They claim lichenometry can accurately date an earthquake to within ten years and note this requires careful site selection and accurate calibration of lichen growth rates, stating that the method is best used for earthquakes that occurred within the last 500 years. The last sentence states certain conditions must be minimized because they affect normal lichen growth, and things like wind and shade that accelerate lichen growth must be factored in.

A. No.  This states while lichenometry is less accurate when it is used to date earthquakes that occurred more than 500 years ago, it is still more accurate than other methods for dating such earthquakes. Remember that an assumption should bolster the statements. This does nothing to bolster the given statements, and furthermore, other methods really aren’t a part of these statements.

B. No.  This states there is no reliable method for determining the intensity of the radiation now hitting Earth’s upper atmosphere. This issue is something mentioned earlier in the third paragraph in regards to radiocarbon dating, not lichenometry.

C. No.  This states lichens are able to grow only on the types of rocks that are common in mountainous regions. Types of rocks are nota factor in the passage.

D. No.  This states the mountain ranges that produce the kinds of rockfalls studied in lichenometry are also subject to more frequent snowfalls and avalanches than other mountain ranges are. Be careful on this one. The statements the author gives state these conditions must be minimized at sites, so it’s okay if these conditions still occur. However, Bull and Brandon aren’t assuming that these ranges are subject to these conditions, only cautioning that certain factors must be adjusted for.

E. Yes.   This states the extent to which conditions like shade and wind, which have affected the growth of existing lichen colonies, can be determined. You see in the final sentence that shade and wind must be factored in because they accelerate the growth of lichens. So, it must be assumed such effects can be determined.

Answer: E

Sajjad1994 · Answer

8. Given the information in the passage, to which one of the following would lichenometry likely be most applicable?

Explanation

The question asks you to determine to which situation lichenometry would most likely be applicable. Lichenometry involves measuring lichen growth on newly exposed rock surfaces. So, you want to find something that fits with this description.

A. No.  This states identifying the number of times a particular river has flooded in the past 1,000 years. The second paragraph states lichenometry studies lichen growth on rocks. So, it would not appear it could be applied to a flood situation.

B. No.  This states identifying the age of a fossilized skeleton of a mammal that lived many thousands of years ago. The third paragraph states lichenometry is best used for earthquakes that occurred in the last 500 years.

C. No.  This states identifying the age of an ancient beach now underwater approximately 30 kilometers off the present shore. Because lichenometry involves the study of lichen growth, it’s uncertain how this would apply to water situations.

D. Yes.   This states identifying the rate, in kilometers per century, at which a glacier has been receding up a mountain valley. You know that lichenometry focuses on the rate of lichen growth on rocks. So, it would seem to apply to this situation, as rock surface would be exposed as the glacier recedes.

E. No.  This states identifying local trends in annual rainfall rates in a particular valley over the past five centuries. Once again, the focus here is on water, and water doesn’t appear to affect lichen growth, so lichenometry doesn’t seem to be applicable.

Answer: D

To study centuries-old earthquakes and the geologic faults that caused

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To study centuries-old earthquakes and the geologic faults that caused

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615 to 715 in 15 Days (Ria's Strategies)

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My Rewards