Convection currrents in the mantle, it was proposed, would bring magma up to the surface, make new ocean floor, and then the currents would drive the two halves of the ocean floor in opposite directions. But the notion of subduction zones and tectonic plates would develop quite rapidly, once geophysicists were convinced of the reality of seafloor spreading, as they soon were.
Most of our images today are diagrams from this seminal article. One shows a cross-section of an oceanic ridge, with newly formed oceanic floor on either side fourth image, above ; another proposes a possible pattern for convection currents in the mantle fifth image, just above , and a third shows volcanoes, atolls, and guyots as they move away from a ridge and subside sixth image, below.
The only interesting portrait of Hess is a photo taken during his World War II days, but the only available version is small. We use it anyway, because in all the other photographs, he looks like, well, a mild-mannered university professor, and not at all like someone who set off a revolution in the earth sciences.
This post is greatly indebted to the third volume of The Continental Drift Controversy , written by my good friend and sorely missed colleague, Hank Frankel. If you would like to continue the story of Harry Hess and seafloor spreading, you might want to read his post on the man who first proposed transform faults and tectonic plates, Tuzo Wilson , a post that Hank wrote shortly before his sudden death.
William B. Ashworth, Jr. Comments or corrections are welcome; please direct to ashworthw umkc. Scientist of the Day - Harry Hess May 24, Hess discovered that the oceans were shallower in the middle and identified the presence of Mid Ocean Ridges , raised above the surrounding generally flat sea floor abyssal plain by as much as 1. In addition he found that the deepest parts of the oceans were very close to continental margins in the Pacific with Ocean Trenches extending down to depths of over 11 km in the case of the Marianas Trench off the coast of Japan.
This created new seafloor which then spread away from the ridge in both directions. The ocean ridge was thermally expanded and consequently higher than the ocean floor further away. There still seemed to be no way that continents could plow through the earth's surface on their own, but perhaps something else could explain how the land masses had once been joined. Part of his mission had been to study the deepest parts of the ocean floor.
In he had discovered that hundreds of flat-topped mountains, perhaps sunken islands, shape the Pacific floor. The discovery of the Great Global Rift in the s inspired him to look back at his data from years before. After much thought, he proposed in that the movement of the continents was a result of sea-floor spreading.
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