How an “Essay in Geopoetry” Led to the New Science of Plate Tectonics
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1946–1966 • 273 September 24, 1979 FITZ GORO / LIFE TIME INC. Geologist Harry Hess *31 saw that convection currents from deep within the earth provided the driving force behind continental drift. H ESS’ S GEOLOGICAL REVOLUTION How an “essay in geopoetry” led to the new science of plate tectonics By J. I. Merritt ’66 n the evening of March 26, 1957, faculty and stu- vary, but in essence this is what he said: “Thank you, Bruce, dents of Princeton’s Geology Department gathered for a lecture that shakes geology to its very foundations.” O in 220 Guyot Hall for a lecture on the latest in a Hess’s colleagues, who shared his orthodox views of earth series of discoveries that were soon to revolutionize the earth history, puzzled over these remarks—could he possibly mean sciences. Bruce Heezen, a respected geologist from what he said? Three years later they would recall his words Columbia’s Lamont Geological Observatory, had been in- when he circulated a paper he had written incorporating vited to speak on recent evidence from ocean soundings that Heezen’s concept that the oceans were young and growing. a continuous “rift” or valley ran along the crest of an under- Instead of accepting the theory of an expanding earth, how- water mountain chain known as the Mid-Atlantic Ridge. ever, Hess suggested the following: Heezen proposed that this rift and others like it, by extrud- • The new crustal material created at the mid-ocean ridges ing magma, or molten lava, had been creating ocean floor was eventually consumed in what he called the “jaw crusher” for the last 200-300 million years. Before then, he said, no of deep ocean trenches like those lying along much of the oceans had existed—a single great continent had covered western Pacific basin. the planet, and the earth had been only about half of its • It was convection—the slow circulation of hot, present size. semimolten rock from the earth’s interior—that powered this While many in the audience were willing to accept that crustal movement. rifts indeed existed along the world’s ocean ridges, the idea • The continents, which were once welded together but that the earth had somehow expanded like a balloon to ac- had been split apart by this great convection engine, were fixed commodate its oceans seemed patently absurd. When Heezen in the earth’s spreading crust and rode along like rocks im- finished there was polite applause, followed by silence. Then bedded in moving glacial ice. Harry Hess *31, the department chairman and Heezen’s host Thus Hess’s grand scheme made sense out of the neat fit of for the evening, stood up in the back of the room. Accounts land masses such as South America and Africa, long noticed 274 • T HE BEST OF PAW by geologists and laymen alike but never satisfactorily explained trenches to outer space. Hess championed a project, called until then. “Mohole,” to drill four miles deep into the earth, and he was The Hess paper—innocuously titled “History of Ocean Ba- among the select group of geologists to examine the first moon sins” and described by him as “an essay in geopoetry”—was rocks brought back by Apollo astronauts. And his sense of eventually published in 1962 as part of a volume honoring justice compelled him, virtually alone among scientists of stat- Princeton geologist Arthur F. Buddington *16. In the interim, ure, to speak publicly on behalf of the controversial Immanuel a government geologist named Robert Dietz developed, inde- Velikovsky—not because Hess believed Velikovsky’s crack- pendently of Hess, a similar theory and applied the term “sea- pot theories about a near collision between Earth and Venus floor spreading” to the earth’s crustal dynamics. Others soon (he didn’t) but because, as he told him, “You deserve a fair began building on the framework constructed by Hess and hearing.” Dietz, including two young Princeton geologists, Frederick Vine Although primarily a mineralogist whose reputation be- and Jason Morgan *64, who would make significant contribu- fore 1960 rested on his studies of silicate rocks, Hess from tions in their own right to the new science that by 1967 was the beginning of his career maintained a related interest in known as plate tectonics. the ocean floor. After graduating in 1927 from Yale (where The model as fleshed out showed that the earth’s crust was he claimed to have failed his first mineralogy course and was divided into approximately 20 sections, told he had no future in that field), he or plates, whose interactions could help took his doctorate at Princeton and in to explain many long-standing questions 1931 joined an undersea expedition about mountain building, earthquakes, with the eminent Dutch geophysicist ore concentrations, and the similarity of Felix Vening Meinesz. During this and fossils between widely separated conti- subsequent investigations of the ocean nents. A scientific revolution—owing in bottom, Hess was encouraged by his no small measure to Hess’s insight and mentor on the Princeton faculty, the leadership—was underway. A trace of the Pacific floor, obtained by Hess flamboyant Richard M. “Dicky” Field, Years after his death, Harry Ham- with a depth recorder aboard the navy ship he an early proponent of deep-sea explo- commanded in World War II, showing one of mond Hess remains a larger-than-life ration. While no theoretician, the out- the flat-topped seamounts he named guyots, figure. Anecdotes about him abound in after Princeton geologist Arnold Guyot. going Field was a catalyst and organizer Guyot Hall, the crenellated, turn- who brought together many of the of-the-century home of the university’s Department of Geo- people, including Hess and Meinesz, who would play critical logical and Geophysical Sciences, where he was a fixture for 40 roles in the development of plate tectonics. years. A quiet, unpretentious man with a small mustache and Meinesz, a huge man who could barely squeeze into the tiny a constantly lit cigarette, he worked out of an office of leg- submarines of his day, was fascinated by the so-called “gravity endary clutter, whose every surface was piled high with pa- anomalies” that existed along the trenches of island arcs in the pers and hydrologic charts. He had tremendous powers of East and West Indies. Using a highly sensitive pendulum concentration, and his wife, Annette, recalled his ability to gravimeter, he charted the gravitational pull along the ocean think exclusively about geology “from the time he woke up in floor and found, contrary to a fundamental geophysical law, the morning until he went to bed.” The one vacation she could that it was remarkably weaker over the trenches. These anoma- remember away from geology was their honeymoon on Nan- lies would puzzle Hess and others for three decades but would tucket: “The island has only one rock, and that was brought finally be explained by the new theory of plate tectonics: the in as a monument. He used to look at it longingly.” weakness of gravity over the trenches resulted from the con- Hess had a wonderfully unpredictable sense of humor. At a vective force that was pulling the edge of the sea floor down banquet celebrating the end of a field trip to Russia by Ameri- into the earth. can geologists in 1937, vodka was flowing freely. Suddenly To carry out his work on U.S. submarines Hess joined the Hess leaped onto the table and proposed a toast: “Here’s to Navy Reserve, a seemingly routine act but one fraught with the Revolution! . The Hercynian Revolution!”—a reference later consequences. On the day after the Japanese attack on to the geological event that had thrust up the Urals. Pearl Harbor he put on the one Navy uniform he owned and His professional interests ranged from the deepest ocean took the 7:42 a.m. train to New York to volunteer for active 1946–1966 • 275 duty. He was soon in charge of estimating the daily positions The mantle was actually composed of a series of convection of German submarines in the Atlantic. Later in the war he cells whose boundaries were marked on the surface by ocean transferred to sea duty, taking part (eventually as captain of ridges and trenches. In an endless cycle, the heated rock in the the assault transport U.S.S. Cape Johnson) in landings in the cells rose toward the surface, then cooled and descended to a Marianas, Leyte, Linguayan Gulf, and Iwo Jima. depth where it took on more heat and began to ascend again. During his time at sea Hess made a remarkable discovery. “The mid-ocean ridges could represent the traces of rising limbs For research purposes he had a special deep-sea fathometer of convection cells,” Hess wrote, while the belt of trenches and installed on his ship and ordered that it be kept on all the time mountains ringing the Pacific would represent descending during his frequent criss-crossings of the Pacific. He thus ac- limbs. The continents “ride passively on mantle material as it cumulated some 250,000 miles of soundings and found that comes to the surface at the crest of the ridge and then move the Pacific bottom was studded with at least 160 flat-topped laterally away from it.” seamounts rising to within 3,000 feet of the surface. He called While new evidence and theories have emerged since Hess’s these structures “drowned ancient islands” and named them paper to show that the driving mechanism is far more compli- guyots, after Arnold Guyot, the Swiss geologist who founded cated than the simple model he outlined, the basic concept of Princeton’s department in the mid-19th century.