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

Kindly provide official explanation for q4 and q8

kindly help with 4th and 8th

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.

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

#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

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 ?

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.

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