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# Prior to 1965 geologists assumed that

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Prior to 1965 geologists assumed that [#permalink]

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02 Oct 2013, 11:08
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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 each other, 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 suggests which of the following regarding Henyey’s findings about temperature in the San Andreas Fault?
A.Scientists have yet to formulate a definitive explanation for Henyey’s findings.
B.Recent research suggests that Henyey’s explanation for the findings should be modified.
C.Henyey’s findings had to be recalculated in light of Byerlee’s 1992 experiment.
D.Henyey’s findings provided support for an assumption long held by geologists.
E.Scientists have been unable to duplicate Henyey’s findings using more recent experimental methods.

The passage is primarily concerned with
A.evaluating a method used to test a particular scientific hypothesis
B.discussing explanations for an unexpected scientific finding
C.examining the assumptions underlying a particular experiment
D.questioning the validity of a scientific finding
E.presenting evidence to support a recent scientific hypothesis

The passage mostly agree 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

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Re: Prior to 1965 geologists assumed that [#permalink]

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12 May 2015, 01:04
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Re: Prior to 1965 geologists assumed that [#permalink]

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12 May 2015, 02:49
Request the GC community to use spoilers, to conceal the answer key.

1: A. First thing to note is that Henyey just had "findings" and he did not offer an "explanation". So, B is out. His finding was that temperatures in drill holes near the fault were not as elevated as had been expected. Initially scientists thought that “weaker” materials, such as clays, were the reason for low temperatures; Byerlee proved that clay would also produce elevated temperatures. So, clearly, presence of clay did not provide an explanation to Henyey's findings". So, an alternate explanation needed to be looked at.

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 ends here. So, clearly this entire episode is still at a "wondering" stage. In other words, Scientists have yet to formulate a definitive explanation for Henyey’s findings.

2: B. The expectation was that two giant rock plates meeting at the San Andreas Fault would generate heat through friction. However, unexpected scientific finding was that Henyey did not find temperatures as elevated as had been expected. The whole passage that discusses explanation for this unexpected scientific finding.

3: D. First sentence of the passage is an assumption by geologists. Heney’s findings are counter to those assumptions.
Re: Prior to 1965 geologists assumed that   [#permalink] 12 May 2015, 02:49
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