GMAT Prep RC Prior to 1965 geologists assumed..

[supratim7]

Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through friction as they grind past eachother, but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected. Some geologists wondered whether the absence of friction-generated heat could be explained by the kinds of rock composing the fault. Geologists' pre-1965 assumptions concerning heat generated in the fault were based on calculations about common varieties of rocks, such as limestone and granite; but "weaker" materials, such as clays, had already been identified in samples retrieved from the fault zone. Under normal conditions, rocks composed of clay produce far less friction than do other rock types.

In 1992 Byerlee tested whether these materials would produce friction 10 to 15 kilometers below the Earth's surface. Byerlee found that when clay samples were subjected to the thousands of atmospheres of pressure they would encounter deep inside the Earth, they produced as much friction as was produced by other rock types. The harder rocks push against each other, the hotter they become; in other words, pressure itself, not only the rocks' properties, affects frictional heating. Geologists therefore wondered whether the friction between the plates was being reduced by pockets of pressurized water within the fault that push the plates away from each other.

The passage mostly agrees that Heney's findings about temperature in the San Andreas Fault made the greatest contribution in that they
A. revealed an error in previous measurements of temperature in the San Andreas Fault zone
B. indicated the types of clay present in the rocks that form the San Andreas Fault
C. established the superiority of a particular technique for evaluating data concerning friction in the San Andreas Fault
D. suggested that geologists had inaccurately assumed that giant rock plates that meet at the San Andreas Fault generate heat through friction
E. confirmed geologists’ assumptions about the amount of friction generated by common varieties of rocks, such as limestone and granite

OA (D)

Whew!! did a spell-check, but some typo may still be there..

Got this one wrong. Selected "C", not "D" for following reasons..

For C:
The passage says "Byerlee found that clay when subjected to lot of pressure, produced as much friction as was produced by other rocks. Pressure itself, not only the rocks’ properties, affects frictional heating".

Isn't taking pressure into account a better technique to evaluate data concerning friction??

Against D:
The passage says "Byerlee found that clay when subjected to lot of pressure, produced as much friction as was produced by other rocks. Pressure itself, not only the rocks’ properties, affects frictional heating".

Old thought: Rock type » Friction » Heat.
Byerlee: Rock type + Pressure » FRICTION » Heat. Ultimately heat is getting generated through "friction".

If the choice read "suggested that geologists had inaccurately assumed that giant rock plates that meet at the San Andreas Fault generate heat through friction ONLY" then I would have considered D.

OA is OA :) So, where did I miss it??

Many thanks | Supratim

[messi10]

hmmm, I think you are looking too far down the passage. The question is asking about Henley's findings, not the passage as a whole. The answer is in the first sentence:

Prior to 1965 geologists assumed.........[details]..........., but in 1965 Henley found that.........[details]

The wording in first line tells you that some change is coming up and then the "but" confirms it. As far as Henleys contribution goes, thats all you need

[tim]

Thanks. Yeah, D is the answer because Henyey used actual data to demonstrate that the assumption of heat was invalid. C is no good because there is no technique that has been demonstrated to be superior here.

Was this really only a one-paragraph passage in the original?

[supratim7]

hmmm, I think you are looking too far down the passage. The question is asking about Henley's findings, not the passage as a whole.

Sorry mate, I don't get it.
The stem is "The passage mostly agree that Henley’s findings about.." So, (a) how can we disregard the passage as a whole and just go after Henley? (b) I thought, many RC inferences tend to assimilate/integrate two bits of info mentioned in separate portions of the passage.

Thanks. Yeah, D is the answer because Henyey used actual data to demonstrate that the assumption of heat was invalid. C is no good because there is no technique that has been demonstrated to be superior here.

Tried couple of times.. couldn't unpack your logic/explanation/argument.

Was this really only a one-paragraph passage in the original?

My bad.. missed para break at "In 1992 Byerlee tested.."

[messi10]

Hi supratim,

Its not disregarding the passage when you are looking in a specific place for a question that has asked about a specific thing. Its just concentrating on the part that you have to. If the question stem stated "Which of the following inferences is the author most likely to agree to?" then you need to consider the passage as a whole.

The question stem here is asking for Henyeys contribution so you have look where Henyey is mentioned.

If you look at the wording of answer choice D, it is just a restatement of the first sentence:

Prior to 1965, geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat Line through friction as they grind past each other, but in 1965 Henyey....blah blah....

Answer choice C is just plain wrong cause there is no superiority of any technique that has been established.

Inference questions on the GMAT are very subtle and almost a restatement of whats already present in the passage. They don't work like real life inference where you make small 'common sense' leaps to make conclusions

Also, the reason you have crossed of answer choice D is another reason why you shouldn't be looking at the whole passage to answer this question. Because according to the whole passage, answer D is actually incorrect. In the end, it is still friction that's causing the heat. Its just that pressure, which was previously not considered, is now considered a factor that contributes to the force of the friction.

Hope this helps

[supratim7]

Hi messi,
Thank you for the reply.

Answer choice C is just plain wrong cause there is no superiority of any technique that has been established.

You do have a valid point against C.

C. established the superiority of a particular technique for evaluating data concerning friction in the San Andreas Fault

The passage says "Byerlee found that clay when subjected to lot of pressure, produced as much friction as was produced by other rocks. Pressure itself, not only the rocks’ properties, affects frictional heating".

Isn't taking pressure into account a better technique to evaluate data concerning friction??

"taking pressure into account" is surely an ADDITIONAL technique that brought in new info/data but not necessarily a SUPERIOR one... aaargh.. my bad.

Thank you for the insights.. Appreciate it :)

[jnelson0612]

It's great to see students helping each other! :-) Let us know if you need anything else.

[supratim7]

Thank you for asking jnelson :)
I am good with this one; messi10's reply helped.

Many thanks | Supratim

[tim]

:)

[arnabgangully]

Inference questions on the GMAT are very subtle and almost a restatement of whats already present in the passage. They don't work like real life inference where you make small 'common sense' leaps to make conclusions

Wow messi perfect I will remember this it helped.

[tim]

cool.

[sheetal_virmani]

I chose A because Henyey's findings revealed that there was a huge temperature mismatch between what was thought earlier and what it actually was. The heat was still generated through friction itself. Hence, I chose A over D.
Could you please help?
Thanks!

[RonPurewal]

there was a huge temperature mismatch between what was thought earlier and what it actually was

you are correct about this ... and, that's actually the reason why (a) is incorrect.

(a) contains the idea that earlier measurements were inaccurate. the passage doesn't mention any earlier measurements at all -- as you've just written here yourself, the earlier temperature estimates were just guesses/hypotheses, based on this idea of friction.

[sheetal_virmani]

Yep, makes sense! Thanks Ron!

[tim]

:)