#4 - Must Be True

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=14432)

The correct answer choice is (B)

This question asks for a response that is most strongly supported by the passage, so we must find
an answer choice that is consistent with the author’s reasoning. Because the question stem does
not contain a location indicator, the most efficient approach would be to review the answer choices
and quickly eliminate any that are inconsistent with the passage. When examining the remaining
responses more closely, consider passage organization first—this will help you locate the specific
paragraph(s) that validate your answer.

Answer choice (A): At the end of the first paragraph, the author indicates that radiocarbon dating
can provide hints about the likelihood and location of future earthquakes. However, we are given
no information as to how lichenometry compares to radiocarbon dating in this respect. A direct
comparison between the two methods is made in the third paragraph of the passage, but only with
respect to each method’s accuracy of dating past earthquakes, not of predicting future ones.

Answer choice (B): This is the correct answer. According to the information presented in the
first paragraph, radiocarbon dating involves digging “trenches along visible fault lines, looking for
sediments that show evidence of having shifted” (lines 3-4). Clearly, without identifiable fault lines,
seismologists would have difficulty finding sediments in which organic material was trapped during
an earthquake. The fact that radiocarbon dating requires fault-line sediments can also be inferred
from its comparison to lichenometry in the second paragraph (lines 21-23).

Answer choice (C): The passage provides no evidence to support the claim that radiocarbon dating
and lichenometry are currently the only viable methods of detecting and dating past earthquakes. Just
because no other methods were discussed does not mean that such methods do not exist.

Answer choice (D): According to lines 45-48, radiocarbon datings of events that occurred during the
past 300 years are of little value. Lichenometry, on the other hand, is best used for earthquakes that
occurred within the last 500 years (lines 53-54). On the basis of this information, we can conclude
that both lichenometry and radiocarbon measurements would be relatively accurate in dating
earthquakes that occurred approximately 400 years ago, but there is no evidence to support the claim
that radiocarbon dating would be more accurate than lichenometry in this respect.

Note that just because lichenometry is best used for earthquakes that occurred within the last 500
years does not make it the best method for dating such earthquakes. Nevertheless, there is no
evidence that radiocarbon dating would be any more accurate than lichenometry.

Answer choice (E): At first glance, this seems like an attractive answer. In the third paragraph, Bull
and Brandon urge caution in carefully selecting sites that minimize the influence of “disturbances
that would affect lichen growth” (lines 55-57). However, this does not mean that lichenometry is
altogether useless in regions where such disturbances do occur. Furthermore, note that the occurrence
of conditions that accelerate lichen growth does not preclude the usefulness of lichenometry, as long
as such conditions can be “factored in” (line 58).

[moshei24]

Hi, I got this question right, but when I look over it, it seems like (E) also works. The wording seems to match up to the wording in the passage. The passage says that "sites must be selected to minimize the influence..." and the answer says "the usefulness...is limited to geographic regions where factors...generally do not occur." Is the difference in the fact that the answer says geographic regions, while the passages says sites? Because in a geographic region where these factors occur, there still might be a good site? Can you explain this question, please?

Thanks!

[Steve Stein]

You basically got it--choosing sites to minimize the influence of certain factors is not the same as limiting yourself to places where those factors don't exist at all. If, for example, factors that would affect normal lichen growth exist everywhere, then you could still seek to find places where those factors are at a minimum.

I hope that's helpful--let me know. Thanks!

~Steve

[moshei24]

Right, so it exaggerated by saying no factors as opposed to saying minimal factors.

Thanks!

[Margo]

I initially fell for the trap in E for this question, but looking back I can see why B is correct.

However, I hesitated in choosing B. The answer says that radiocarbon dating is "unlikely to be helpful" if no fault lines are present, but the passage states that to study earthquakes, they "usually" dig trenches along visible fault lines (lines 2-3). The passage doesn't rule out the possibility that perhaps radiocarbon dating can be helpful in certain circumstances besides in fault lines...but I guess this is an example of a question where the answer isn't perfect, but just the best available?

In other words, I feel like I'm making a hasty assumption by concluding that radiocarbon dating isn't helpful in any other circumstances but X just because X is the only circumstance they refer to here. Sorry if I'm nit-picking, just trying to understand! Thanks

[Adam Tyson]

You're right about B being the best answer, even if less than perfect, Margo, but there IS evidence that radiocarbon dating would be unlikely to be helpful without a visible fault line, and that is that without a visible fault line showing us where shifts took place, how would we connect whatever organic matter we found to an earthquake? It's only because the organic matter is trapped in an area where the faults moved that dating it tells us anything about earthquakes! Otherwise, all we would likely learn from an old piece of wood, would be how old that piece of wood was, with no way to connect it to an earthquake. At least, that's what the explanation of radiocarbon dating seems to be saying at the beginning of the passage - that the location of a known earthquake, correlated with the age of the material found at that known location, can tell us when the quake occurred.

While that may not be entirely satisfactory, and we might be able to use radiocarbon dating in some other way to date earthquakes, answer B remains the best of the bunch and the one we must select! Sometimes that's all we can do on this test!