Prior to 1965 geologists assumed that the two giant rock plates meeting at the San Andreas Fault generate heat through...
GMAT Reading Comprehension : (RC) Questions
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?
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| 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 | What it says: Before 1965, scientists thought that when two huge pieces of rock rub against each other at the San Andreas Fault, they create heat from the friction. What it does: Sets up the "old thinking" or baseline assumption that we'll build from Source/Type: Historical scientific assumption (what geologists believed) Connection to Previous Sentences: This is our starting point - no previous information to connect to yet Visualization: Imagine rubbing your hands together rapidly - they get warm from friction. Geologists thought the same thing happened with massive rock plates grinding past each other. What We Know So Far: Scientists had a theory about friction creating heat at fault lines What We Don't Know Yet: Whether this theory was correct, what happened in 1965 Reading Strategy Insight: This is classic RC setup - establishing the "before" so we can understand the "after" |
| but in 1965 Henyey found that temperatures in drill holes near the fault were not as elevated as had been expected | What it says: But when Henyey actually measured temperatures by drilling holes near the fault, they weren't as hot as the theory predicted. What it does: Introduces the key problem/contradiction that drives the whole passage Source/Type: Researcher's empirical findings (Henyey's actual measurements) Connection to Previous Sentences: This directly contradicts the previous assumption - the "but" signals that reality didn't match theory Visualization: Expected temperature: 180°F, Actual measured temperature: 120°F (not as hot as predicted) What We Know So Far: • Old theory: Friction should create significant heat • 1965 reality check: Actual temperatures were lower than expected What We Don't Know Yet: Why the temperatures were lower, what explanations scientists proposed Reading Strategy Insight: This is the central puzzle the entire passage will try to solve |
2. Passage Summary:
Author's Purpose:
To trace the scientific investigation into why temperatures at the San Andreas Fault were lower than expected, showing how geologists tested and revised their explanations over time.
Main Point:
Scientific understanding of the San Andreas Fault has evolved from simple assumptions about rock friction to more complex explanations, with scientists now considering that pressurized water might be reducing friction and heat generation between the rock plates.
3. Question Analysis:
The question asks what the passage suggests regarding Henyey's findings about temperature in the San Andreas Fault. This is asking us to identify what conclusion we can draw from the passage about the status or significance of Henyey's 1965 discovery that temperatures were lower than expected.
Why It's Right:
• The passage shows multiple attempts to explain Henyey's findings without reaching a definitive conclusion
• The rock type explanation was tested and ultimately ruled out by Byerlee's research
• The passage ends with scientists "wondering" about pressurized water, indicating continued uncertainty
• The phrase "wondered whether" suggests hypothesis formation, not established explanation
Key Evidence: "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 word "wondered" indicates ongoing uncertainty, not a definitive explanation.
Why It's Wrong:
• The passage doesn't describe Henyey providing any explanation for his findings - he simply measured temperatures
• Recent research (Byerlee's) tested a different explanation (rock types), not Henyey's explanation
• Henyey discovered the anomaly; he didn't propose the clay explanation that was later modified
Why It's Wrong:
• Byerlee's experiment tested clay behavior under pressure, not Henyey's temperature measurements
• There's no indication that Henyey's temperature data needed recalculation
• Byerlee's work addressed theoretical explanations for the temperatures, not the temperature measurements themselves
Why It's Wrong:
• Henyey's findings contradicted, rather than supported, geologists' long-held assumptions
• The passage clearly states temperatures were "not as elevated as had been expected"
• This discovery challenged existing assumptions about friction-generated heat
Why It's Wrong:
• There's no mention of other scientists attempting to duplicate Henyey's findings
• The passage doesn't discuss any problems with replicating his temperature measurements
• The focus is on explaining his findings, not on verifying them through duplication