If early twentieth-century geologists and geo-physicists had heeded the fundamental axiom of the Greek philosopher Heraclitus. “Everything flows.” the sterile and sometimes bitter controversy that divided them in the first half of the twentieth century might have been avoided.
At the time, some geologists argued that the history of past climates, reconstructed from examination of rock strata, and the distribution of past fauna, documented through analysis of the fossil record, were inexplicable if the continents had never moved. Noting that some of the continents could be fitted together reasonably well as a kind of crustal jigsaw puzzle, they theorized that during some part of the Earth’s history, the continents must have moved.
Geophysicists, looking at different types of data, reached a very different conclusion. When a major earthquake occurred, they noted, the Earth behaved like a gigantic bell struck by a hammer. it rang, and the reverberations echoed around the Earth for several hours thereafter. They inferred from this that the outer part of the Earth was strong and rigid. This inference seemed to be confirmed by the evidence of mountains. Rocks at the base of mountains like ten-kilometer-high Everest had to be able to withstand enormous stress or they would crack and the mountains collapse. Because the height of any structure is limited by the strength of its supporting materials, the stability of mountains seemed to corroborate the geophysicists’ conclusion: the Earth was simply too strong for the continents to move.
There followed a classic confrontation, pitting “movement” against “rigidity,” which in retrospect need never have occurred. The “strength paradox” had been familiar to generations of geologists from the study of rock deformations in mountain belts, where it had been observed that some quite rigid rocks had in the past been highly ductile, on occasion even viscous. But both geologists and geophysicists failed to connect this evidence with a phenomenon they knew in the context of practical problems of structural engineering “creep”. Creep is observed in materials that are subjected to relatively low stresses for very long periods of time; the materials deform continuously, but very slowly, like fluids with an extremely high viscosity. The process operates most rapidly in materials near their melting point.
Thus, before talking of the “strength” of rocks, both groups of scientists should have known something of the temperature of the rocks they were studying and should have specified the time scale under consideration. Rocks at the Earth’s surface are between 600Ā° and 1,000Ā° C below their melting temperatures and thus creep so slowly that even on geological time scales of millions of years, they may be regarded as brittle and strong solids. Within the Earth, however, temperature increases relatively rapidly with depth and, below a few hundred kilometers, creep occurs so readily that on time scales of more than a few million years, rocks underneath the Earth’s crust must be considered as fluids even though they are perfectly normal crystalline solids.
Question 1
The author of the passage is primarily concerned with
A. presenting new evidence
B. correcting an oversimplification
C. analyzing the reasons for a dispute
D. reinterpreting a theory
E. resolving a dispute between past and present views
Question 2
It can be inferred from the passage that all of the following are true of the phenomenon of creep EXCEPT:
A. The effects of creep on normal crystalline solids are always imperceptible.
B. The rate of creep is increased by raising the temperature of a solid.
C. Creep occurs even in relatively large geological structures.
D. Creep operates most rapidly on rocks near their melting point.
E. Creep occurs both on and below the Earth’s surface.
Question 3
The passage suggests that the author considers the disagreement between early twentieth-century geologists and geophysicists to have been
A. confusing
B. inevitable
C. surprising and inexplicable
D. hostile but ultimately useful
E. needless and unproductive
Question 4
According to the passage, the theoretical position of early twentieth-century geologist was based on which of the following?
- The shapes of the Earth’s continents
- The evidence of ductility in rocks
- The fossil record
A. I only
B. III only
C. I and II only
D. I and III only
E. I, II, and III
Question 5
It can be inferred from the passage that which of the following statements best expresses the “strength paradox”?
A. Some rocks arc rigid and brittle, whereas others are fluid and ductile depending on their chemical composition.
B. Rocks at the base of mountains may be very rigid while rocks higher up the mountain are more fluid.
C. The rigidity of the same rock can vary widely depending on the physical stresses acting on it.
D. Rocks in scene locations on the Earth’s surface are far more rigid and brittle than are other rocks subjected to comparable stress.
E. The strength of rocks in mountain belts varies according to the rate of creep in a particular location.
Question 6
According to the author of the passage, geologists and geophysicists could have resolved their theoretical argument if they had
A. more carefully reviewed the fossa evidence
B. closely examined the physical appearance of the Earth’s surface rock
C. applied their knowledge of the effects of stress to the geological evidence
D. known about the phenomenon of creep
E. understood more completely the effects of phenomena such as earthquakes
Question 7
The author suggests that the major reason for the disagreement between early twentieth-century geologists and geophysicists was that each group
A. reached conflicting conclusions from separate analyses of the fossil record
B. interpreted the evidence of rock deformations differently
C. examined data on different kinds of phenomena
D. based their respective theories on conflicting estimates of the Earth’s age
E. made different though equally inaccurate assumptions about the Earth’s history
Question 8
Which of the following best describes the organization of the passage?
A. A particular view of a scientific issue is outlined and arguments against that view are stated.
B. A theory is presented, relevant new evidence is discussed, and the theory is reinterpreted.
C. A scientific dispute is examined and possible resolutions of the dispute are outlined
D. A hypothesis is stated and new evidence proving its validity is presented.
E. A scientific dispute is summarized and reasons for its occurrence are offered.
Question 9
Which of the following statements, if true, is most compatible with the principle underlying the geophysicists’ citation of Mt. Everest as evidence for their theories?
A. A one-hundred-story building must have a much stronger base than is necessary for a twenty-story building of similar materials.
B. A thin external material like glass makes a skyscraper less vulnerable to stress from wind than does a thick material like brick.
C. The girders supporting the ceilings and floors on higher levels of a multistory building must be stronger than those supporting ceilings and floors on lower levels.
D. Multistory buildings in earthquake zones must obey height restrictions because of the probability of seismic stress.
E. Buildings with foundations composed of relatively rigid materials art less subject to creep.
Question Analysis:
The question asks us to identify which statement is most compatible with the principle underlying the geophysicists’ citation of Mt. Everest as evidence for their theories. From our passage analysis, we know the geophysicists used Mt. Everest to support their argument that Earth was too rigid for continents to move.
Connecting to Our Passage Analysis:
From our detailed analysis, we understand that the geophysicists’ Mt. Everest argument was:
- Mount Everest is incredibly tall (10 kilometers high)
- The rocks at its base must be extremely strong to support all that weight without cracking
- This demonstrates that Earth’s materials are strong and rigid
- Therefore, Earth is “simply too strong for the continents to move”
The key principle here is that “the height of any structure is limited by the strength of its supporting materials” – meaning taller structures require stronger foundations.
Answer Choices Explained
A. A one-hundred-story building must have a much stronger base than is necessary for a twenty-story building of similar materials.
Why It’s Right:
- Directly parallels the geophysicists’ Mt. Everest reasoning – taller structures require stronger foundations
- Demonstrates the principle that “the height of any structure is limited by the strength of its supporting materials”
- Shows the same proportional relationship: as height increases dramatically (from 20 to 100 stories), foundation strength must increase dramatically
Key Evidence: “Because the height of any structure is limited by the strength of its supporting materials, the stability of mountains seemed to corroborate the geophysicists’ conclusion: the Earth was simply too strong for the continents to move.”
B. A thin external material like glass makes a skyscraper less vulnerable to stress from wind than does a thick material like brick.
Why It’s Wrong:
- Focuses on external materials and wind resistance, not foundational strength supporting vertical load
- Contradicts the Mt. Everest principle by suggesting thinner materials are better for tall structures
- Addresses lateral stress from wind rather than vertical stress from weight
C. The girders supporting the ceilings and floors on higher levels of a multistory building must be stronger than those supporting ceilings and floors on lower levels.
Why It’s Wrong:
- Discusses horizontal support elements (girders for ceilings/floors) rather than foundational support
- Actually contradicts the Mt. Everest logic – higher girders would support less weight, not more
- Focuses on distribution of load across levels rather than total foundational strength
D. Multistory buildings in earthquake zones must obey height restrictions because of the probability of seismic stress.
Why It’s Wrong:
- Introduces earthquake zones as a limiting factor, which is different from the inherent strength principle
- Focuses on external seismic stress rather than the structure’s ability to support its own weight
- Suggests height restrictions due to probability of events, not fundamental material strength limits
E. Buildings with foundations composed of relatively rigid materials art less subject to creep.
Why It’s Wrong:
- Discusses creep resistance, which actually undermines the geophysicists’ position according to the passage
- Focuses on foundations being less subject to deformation over time
- Relates more to the passage’s ultimate resolution about creep than to the geophysicists’ original Mt. Everest argument
