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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 provided the driving force behind .

H ESS’ S GEOLOGICAL REVOLUTION How an “essay in geopoetry” led to the new science of

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 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 , or molten , 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 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 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, 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 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, , 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. convection continues to offer the best explanation for conti- nental drift. hese guyots, which were clearly volcanic in origin and A worldwide network of ultrasensitive seismographs, set up Thad once risen above sea level, would figure prominently in 1960 to monitor the nuclear test-ban treaty, soon offered 15 years later when Hess announced his theory of sea-floor preliminary evidence in support of Hess’s theory. The seismo- spreading and the subduction of the ocean bottom into the graphs recorded that earthquakes along the Pacific deep marine trenches. Research in the 1950s showed that many trench-and-mountain ring occurred on a downward sloping guyots in the mid-Pacific were strikingly young in geologic plane to a depth of 400 miles or more beneath the surface— terms, only 100 million years old, but that those closest to the clearly, some terrible gnashing and grinding was going on down ocean trenches were older and also stood at a slight angle. Hess there. The most startling evidence, however, would come from deduced that guyots and atolls (submerged mountains with coral work by a 24-year-old Cambridge graduate student named growth) were created at the crest of a now extinct mid-Pacific Frederick Vine and his thesis adviser, Drummond Matthews. ridge and were carried away from it by the moving ocean floor. On the basis of some preliminary recordings in the Indian As the guyots approached a trench they rode down toward it, Ocean, Vine and Matthews suggested in 1963 that a perma- tilted on its steeper slope. The guyots were moving away from nent record of continental drift might be found on the ocean the old ridge at a rate of about an inch every five years. floor in the form of magnetic striping. For unknown reasons Hess also pointed to other evidence, such as the surprisingly the earth has periodically reversed its magnetic polarity. When thin layer of on most sea bottom, to show that while lava cools and solidifies, it “locks in” the magnetic lines of force the continents and the ocean’s water were old, the ocean floor in effect at the time. Magma extruded along mid-ocean ridges, was geologically young, which indicated that it was continu- therefore, should record the earth’s polar flip-flops like a mov- ally being created and destroyed. ing film strip. The model of a spreading sea floor was a radical departure Such magnetic striping was confirmed the following year from conventional geological thinking. Although a German with the publication of data from airborne magnetometers off meteorologist named had plumped for a the coast of British Columbia. By 1968, about half the world’s theory of “continental drift” earlier in the century, no satis- ocean floor had been magnetically mapped, and a clear picture factory mechanism for explaining the drift had been found. had emerged of the rate and direction of sea-floor spreading Both Hess and Dietz proposed convection—the circular during the last 150 million years. movement of a heated substance, like hot air rising in a room— In 1965 Hess took a year’s sabbatical at Cambridge, where as the driving force. Elaborating on an idea put forth years he worked closely with Vine, Matthews, and other “drifters”— earlier by his old friend Meinesz, Hess suggested that the as proponents of moving continents were known to their earth’s mantle (the hot, dense layer of rock lying beneath the still-skeptical colleagues. The following year Hess brought Vine crust) had a certain plasticity that under extreme heat and back to Princeton as an instructor. Vine (who in 1971 elected pressure allowed it to move. for family reasons to return to Britain despite a tenure offer 276 • T HE BEST OF PAW from Princeton) shared an office in Guyot Hall with Jason of the earth’s surface as the Afar Triangle in East Africa. At Morgan, a young geophysicist who would soon make brilliant this and similar areas, according to the theory, an upwelling additions of his own to the new theory that was indeed, as plume forms a bulge in the crust. More pressure on the bulge Hess had prophesied nearly 10 years earlier, shaking geology causes it to crack, frequently along three lines radiating from to its foundations. a central point and approximately 120 degrees apart—thus the convergence near Ethiopia and Saudi Arabia of the Afri- organ provided a further clue to understanding the can Rift Valley, the Red Sea, and Gulf of Aden, all of which Mearth’s surface dynamics by applying a mathematical form the border of diverging plates. law called Euler’s theorem, which governs the motion of rigid Geophysicists have also argued that a series of plumes suffi- units on a sphere, to long gashes in the ocean bottom. These ciently close together would form a single volcanic rift like the gashes, known as fracture zones, run at right angles to one that splits the Mid-Atlantic Ridge. It is also believed that mid-ocean ridges and are apparently connected to the phe- sometimes, when a plume cracks the surface, one of the three nomenon of sea-floor spreading. Indeed, geologists had al- lines becomes inactive and forms the basin for a river. Evi- ready matched up the magnetic striping patterns on either dence exists to suggest that the Amazon, Mississippi, and Rhine side of certain Pacific fracture zones and found they are off- rivers resulted this way. set, indicating that sections of once-continuous ocean bot- Unfortunately, we still have little direct evidence concerning tom had been rent apart and separated what goes on deep within the earth, so in some cases by nearly a thousand Morgan’s hypothesis remains just that. miles. There may never be a way of actually Morgan noticed that groups of frac- “proving” the existence of plumes, says ture zones might in fact be segments of Morgan. In sciences like or “small circles” (like lines of longitude on , he explains, discrete experi- a globe), suggesting a common axis ments can be designed to test hypoth- through the center of the earth. This eses, but “proof doesn’t work very well turned out to be the case when he traced in geology.” As a theory, however, the perpendicular lines from a series of frac- plume model conforms to observable ture zones in the South Atlantic and JOHN W.H. SIMPSON ’66 surface phenomena without contradict- Geophysicist Jason Morgan *64 unraveled the found they converged in accordance mystery of fracture zones on the ocean bottom. ing the few existing facts we have con- with Euler’s theorem. A Cambridge cerning the earth’s interior. geophysicist named Dan McKenzie, using different data, ar- A graduate of the Georgia Institute of Technology, Morgan rived at a similar finding concurrently with Morgan. The most earned a doctorate in physics from Princeton and came to ge- important implication of all this was that the fracture zones in ology via (his dissertation concerned the earth’s ro- question resulted from the movement of a rigid unit, or plate. tation and gravitational field). He never took a geology course Largely as a result of the work by Morgan and McKenzie, the and says he is “still learning” about the field. In this regard his term plate tectonics (tectonics meaning movement) came into largely theoretical background could not have been more dif- widespread use at this time. ferent from Hess’s lifelong grounding in mineralogy. During Next Morgan attacked the problem of explaining specifi- his first few years on the faculty, says Morgan, he was very cally how convection drove the plates. Various calculations had much aware of the importance of what Hess was doing but been made to show that the simple convection-cell model of had little to discuss with him professionally. Hess and Dietz was inadequate. Expanding on work by Cana- “I couldn’t understand him,” he recalls. “I was too close to dian geophysicist J. Tuzo Wilson *36, Morgan’s model depicted the physics side of the story. I was becoming aware of the rock huge convection “plumes,” or columns, 100 miles or more in side, but I didn’t really know it at the time. Fred Vine shared diameter, rising from the earth’s deep mantle and spreading the office with me, and in a sense I learned what Hess was like giant thunderheads beneath the asthenosphere, the layer doing through him. Later on I got to know Hess and the rock just below the crustal plates. side better.” First promulgated in 1971, the plume theory has since been Significant work in expanding Morgan’s theory has been done elaborated by Morgan and others to account for such features by another Princeton geologist, Kenneth Deffeyes *59, who 1946–1966 • 277 as a graduate student was present at the 1957 Heezen lecture accomplishments and knew him by sight, but they never met.) and has followed the development of plate tectonics ever since. The revolutionary synthesis achieved by Hess can be traced Deffeyes points out that, while other universities and several to certain personal and professional qualities. “He was a very oceanographic institutes collected much of the data that ulti- able person at the right spot at the right time, and he had enough mately transformed our picture of the world, it was Princeton confidence in himself to make the jump,” says Sheldon Judson and Cambridge that led in interpreting the raw findings and ’40, the department chairman. There was also the breadth and turning them into coherent theory. diversity of his experience, which was “unique—very different “We’ve been criticized at times for not generating the pri- from any other geologist’s at the time.” This included, in the mary data that you get from doing things like radioactive age 1930s, his submarine gravity work over ocean trenches and dating, spectrometer work, or running an oceanographic ship,” land-based studies of peridodite, a volcanic rock that later turned he says. “Other places were collecting and examining the de- out to be a primary component of the ocean floor. Following tails, but Cambridge and Princeton were looking at the larger his wartime discovery of guyots, Hess continued in the Navy picture.” Reserve (eventually making rear admiral) and directed naval efforts at sea-floor mapping. “He had,” adds Judson, “the whole he vision of the earth offered by plate tectonics is the U.S. Navy working for him as a data-collecting agency.” Tmost recent in a series of scientific revolutions, beginning Hess’s open-mindedness was critical to his ability to come with evolution in the mid-19th century and including relativ- to terms with accumulating facts that, by the late 1950s, were ity and quantum mechanics in physics and the breaking of the seriously undermining conventional ideas about the earth. “He DNA code by molecular biologists in the 1950s. In The Struc- had a wonderfully relaxed attitude about being wrong,” re- ture of Scientific Revolutions, a former Princeton historian of members long-time associate Franklyn Van Houten. Despite science, Thomas Kuhn, views science as progressing through Wegener and a school of South African and Australian ge- phases, each governed by a particular “paradigm” or model in ologists who embraced continental drift, scientific orthodoxy effect at the time. Basically, a paradigm is a theory that best could not reconcile it with known physical laws. Like most of explains known data. When new facts come to light that do his peers, Hess for years had dismissed the match between not “fit” the prevailing paradigm, science enters a revolution- land masses as coincidence—even, apparently, up to the eve ary period of confusion and reassessment. Eventually a new of writing his convention-shattering paper on ocean basins. paradigm emerges and another period of what Kuhn calls “nor- About this time Van Houten recalls joking with Hess about a mal science”—working within the framework of an accepted lecture on continental drift he was to give undergraduates: model—begins. Hess remarked, “Don’t tell them that—they won’t believe it.” In the case of geology, a massive amount of new data, much How and when did it click in Hess’s mind that the deep of it a direct result of defense technology, was collected fol- ocean trenches solved the puzzle of sea-floor spreading? lowing World War II. This new information about the ocean “Heezen established that the crust was expanding, and Hess floor, magnetism, , and the earth’s interior pointed used the trenches to get rid of the crust,” says Deffeyes. “But ineluctably to a dynamic model of a convection-driven earth what we were all dying to know was, did Hess give Heezen with a patchwork surface of tearing, crashing, and plunging two years to catch on to the truth, or did it take Hess two years plates. The new paradigm of plate tectonics explained the to catch on?” puzzling postwar facts and opened innumerable fresh lines of The mystery over Hess’s flash of insight remains. On Au- inquiry. In Kuhn’s phrase, geologists today are “mopping up”— gust 26, 1969, he died of a heart attack at the Woods Hole elaborating on the model and filling in gaps, but without radi- Oceanographic Institute, in Massachusetts. It was a month af- cally altering the great schema sketched by Hess in the 1960s. ter the Apollo moon landing, and he was chairing a govern- (Kuhn, who came to Princeton from Berkeley the year fol- ment conference on the future objectives of lunar exploration. lowing publication of The Structure of Scientific Revolutions— Two of the many questions Hess hoped the Apollo missions a milestone in modern intellectual thought—sat on the fac- would answer were whether the moon had ever been volcanic ulty with Hess for five years. He was aware of Hess and his and washed by seas. ■