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Difficulty: MediumDirect Factual Retrieval

In the early 1950s, cartographer Marie Tharp systematically analyzed thousands of bathymetric echo-sounding profiles collected by geologist Bruce Heezen across the North Atlantic seafloor. While plotting the depth measurements, Tharp identified a consistent V-shaped depression running continuously along the crest of the Mid-Atlantic Ridge. She hypothesized that this central notch was a rift valley—a structure created by the tension of oceanic crust pulling apart. Initially, Heezen dismissed her interpretation as an artifact of measurement error, attributing the bathymetric anomalies to localized surface faulting rather than a continuous tectonic boundary.

To test her hypothesis, Tharp sought independent confirmation by cross-referencing her topographic maps with seismic data compiled by colleague Howard Foster. Foster had plotted the precise geographic epicenters of mid-oceanic earthquakes recorded throughout the Atlantic basin. Tharp discovered that these earthquake epicenters aligned almost perfectly with the central axis of her proposed rift valley, rather than dispersing randomly across the abyssal plains. This spatial correlation indicated that active faulting and seismic displacement were concentrated directly within the central notch.

When Heezen presented this overlay of seismic epicenters and topographic profiles at a scientific symposium in 1956, the spatial coincidence convinced many sceptics of the rift valley's physical reality. Nevertheless, widespread acceptance of Tharp's findings within the geological establishment remained slow, largely because the prevailing geophysical paradigm still favored static continental basins over models of dynamic crustal motion.

According to the passage, Marie Tharp took which of the following actions to corroborate her hypothesis regarding the central notch along the Mid-Atlantic Ridge?

  1. She compared her topographic bathymetric maps with plotted locations of oceanic earthquake epicenters.Answer
  2. B
    She re-calibrated the echo-sounding instruments to eliminate data distortions caused by surface faulting.
  3. C
    She plotted an independent series of bathymetric soundings across the abyssal plains of the South Atlantic.
  4. D
    She demonstrated that seismic hypocenters were distributed uniformly throughout the ocean floor.
  5. E
    She published a theoretical paper establishing that continental landmasses expand dynamically over time.

Answer

Marie Tharp corroborated her hypothesis by cross-referencing her topographic depth maps with Howard Foster's mapped locations of oceanic earthquake epicenters.
The correct answer accurately reflects the explicit passage statement that Tharp cross-referenced her topographic bathymetric maps with seismic data mapping the geographic epicenters of mid-oceanic earthquakes to validate her hypothesis.

Step-by-Step Solution

1
Locate the target entity and detail in the passage text
Identify the second paragraph where Tharp's action to test her hypothesis is discussed.
The question specifically asks what action Tharp took to corroborate her hypothesis about the central notch.
2
Extract explicit evidence from the text
The text states: 'To test her hypothesis, Tharp sought independent confirmation by cross-referencing her topographic maps with seismic data compiled by colleague Howard Foster', who had plotted earthquake epicenters.
Direct factual retrieval requires identifying the exact sentence stating the step taken.
3
Match the extracted fact to the paraphrased correct option
Comparing topographic maps with plotted earthquake epicenters is a direct semantic equivalent of cross-referencing topographic maps with seismic data of epicenters.
GMAT correct options paraphrase passage evidence accurately without introducing unsupported claims.

Key Concept

Direct Factual Retrieval from Academic Reading Comprehension Passages
Estimated Time:1m 30s
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Topics

Direct Factual Retrieval

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