Marie Tharp and Bruce Heezen made significant contributions to the development of the theory of plate tectonics through their detailed mapping of the ocean floor. Here is how they found evidence that supported this theory:
1. **Collection of Sonar Data**:
In the post-WWII era, Bruce Heezen, along with other researchers, collected depth measurements of the Atlantic Ocean floor using echo-sounding, or sonar technology. This technology works by sending sound waves from a ship down to the sea floor and recording the time it takes for the echo to return.
2. **Mapping the Mid-Atlantic Ridge**:
As a geologist and oceanographic cartographer, Tharp analyzed the sonar data and began meticulously plotting the depths onto profile sheets to create a visual representation of the ocean's sub-surface topography. She created a series of sounding profiles across the North Atlantic.
3. **Revelation of a Continuous Rift Valley**:
Tharp identified a continuous valley along the crest of the Mid-Atlantic Ridge, which Heezen initially dismissed as "girl talk". Upon closer examination and additional data, they both realized that the valley could be a rift valley — a place where two tectonic plates are moving apart.
4. **Correlation with Earthquake Data**:
Bruce Heezen took it a step further by comparing Tharp's underwater topographical maps with worldwide earthquake distribution maps. They discovered that the global distribution of earthquakes corresponded with the mid-ocean ridges that Tharp had delineated. This correlation suggested that these ridges were sites of high tectonic activity.
5. **Publishing the Findings**:
Despite initial skepticism from the scientific community, Tharp and Heezen published their findings about the rift valley in the 1950s. Their work provided visual and empirical evidence that the sea floor was spreading from these ridges, lending significant support to the development of the plate tectonic theory.
Their findings, together with the magnetometer readings of symmetrical magnetic striping (which recorded the record of geomagnetic field reversals) on either side of the ridges by later scientists, proved pivotal in solidifying the concept of sea-floor spreading proposed by Harry Hess. The eventual acceptance of these ideas, as well as further geological and geophysical evidence, led to the comprehensive model of plate tectonics—the movement of the Earth's lithospheric plates over the asthenosphere—which revolutionized the Earth sciences in the 20th century.
Which of the following describes how Marie Tharp and Bruce Heezen found evidence that led to the theory of plate tectonics?
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