Wegener, Holmes, Dietz, Hess, and Tuzo Wilson

Wegener, Alfred L.                 Meteorologist, astronomer, and Arctic explorer (1880-1930) who popularized Continental Drift Theory. The Germany-born Wegener earned a PhD in astronomy from the University of Berlin in 1904. Despite his training in astronomy, he had always been interested in geophysics and soon became fascinated with the developing fields of meteorology and climatology. Early in his life, he was on the staff of an aeronautical observatory, a professor of geophysics and meteorology at the University of Hamburg (1919-1924), professor of meteorology at the University of Graz (1924-1930), and went on four polar expeditions (1906-1908, 1912-1913, 1929, and 1930) to test his meteorological and geophysical theories. Wegener’s contributions to meteorology include the work, The Thermodynamics of the Atmosphere, which became a standard text throughout Germany and Austria. He was on a meteorological expedition in central Greenland when he was frozen to death in a fierce polar storm.

Perhaps Wegener’s greatest contribution to the scientific world was his ability to weave seemingly dissimilar, unrelated facts into cogent theory. Wegener was one of the first scientists to realize that an understanding of how the Earth works required input and knowledge from all the geosciences rather than one. Today, he is best known for his theory of continental drift, set forth in The Origin of Continents and Oceans, written in 1914 and published originally in 1915 while he was recovering from a wound suffered as a soldier during WWI. According to Wegener, the present continents originally formed one large landmass that he called Pangaea. Over millions of years, Pangaea was subjected to a variety of forces that resulted in it breaking into pieces that separated and drifted apart. His evidence included the matching of certain continental coastlines, including South America and West Africa. In addition, the Appalachian mountains of eastern North America matched with the Scottish Highlands and British Isles and the distinctive rock strata of the Karroo system of South Africa were identical to those of the Santa Catarina system in Brazil. But the strongest evidence was the well-known presence of identical fossils from the same time period that had been found in South America and Africa, especially mesosaurus and glossopteris, as well as matching fossils found in both Europe and North America and Madagascar and India. Those paleontological similarities and the direction and extent of Pensylvanian period continental glaciation in rocks along the coast of South American and Africa proved to Wegener that the now separate land masses had once been joined.

Scientific reaction to Wegener’s theory was almost uniformly hostile and often exceptionally harsh and scathing, partly owing to the fact that he was not trained as a geologist. Rollin T. Chamberlin, a well-known and highly influential geologist at the University of Chicago wrote, “Wegener’s hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories. Its appeal seems to lie in the fact that it plays a game in which there are few restrictive rules and no sharply drawn code of conduct.” William Berryman Scott (1858-1947), an eminent and highly respected vertebrate paleontologist who was Blair Professor of Geology at Princeton and the former president of the influential American Philosophical Society, drove another nail into Wegener’s coffin when he characterized the hypothesis as “utter, damned rot.” Author’s Note: Bold words, those. Would that Scott had been alive in the late 1960s to eat his ridicule when plate tectonics came of age.

Part of the problem was that Wegener proposed no convincing forces that would be sufficient to power continental movement. Wegener theorized that the continents moved through the Earth’s crust like icebreakers plowed through ice sheets, and that the Earth’s centrifugal and tidal forces were responsible. His opponents, especially the well-known and highly reputed British geophysicist and mathematician, Harold Jeffreys (1891-1989), correctly noted that plowing through oceanic crust would distort continents beyond recognition and that the strength and rigidity of the Earth’s mantle over which the drift was taking place were far stronger than the centrifugal and tidal forces suggested by Wegener as the driving forces. Jeffreys castigated Wegener’s theory as “a very dangerous one, and liable to lead to serious error.”

Another problem was that flaws in Wegener’s original data caused his calculations to be incorrect and unreliable. He suggested that North America and Europe were moving apart at over 250 centimeters per year (about ten times the fastest rates seen today and about a hundred times faster than the measured rate for North America and Europe).

Wegener’s ideas were supported by only a few geologists, some of whom were prominent, including the famous Briton, Arthur Holmes; Émile Argand, founder of the Geological Institute of Neuchatel, Switzerland, who observed that continental collisions were the best explanation for the folded and buckled strata in the Swiss Alps; S. William Carey, professor of geology at the University of Tasmania; Lester King, professor of geology at the University of Natal; Professor John Joly, Irish geologist who in 1913 while working in collaboration with Ernest Rutherford used radioactive decay in minerals to estimate that the beginning of the Devonian period was not less than 400 mya, an age that is approximate with that accepted today; Professor Reginald A. Daly of Harvard University (Sturgis-Hooper Professor of Geology); Alexander Du Toit, professor of geology at the University of Johannesburg, South Africa, author of Our Wandering Continents; Amadeus W. Grabau, a geologist and paleontologist at Columbia University and author of several textbooks on stratigraphy and index fossils; Léonce Joleaud, professor of geology at the Sorbonne; and R. D. Oldham, geophysicist and discoverer of the seismic evidence for the Earth’s core. (Author’s Note: John Joly and George Darwin [Charles’s grandson] may have been the first geoscientists to suggest that the Earth’s heat may be partially due to radioactivity.)

That handful aside, influential though they were, the far greater majority of geologists and geophysicists were nearly unanimous in their biting criticism and contemptuous rejection of Wegener’s ideas. The respected American geologists Rollin T. Chamberlin and Harry Fielding Reid and the British geologist Philip Lake wrote highly critical reviews that encouraged a chorus of attacks from other geologists and geophysicists, including some that questioned Wegener’s very competence and credibility as a scientist. Another respected American geologist, Bailey Willis, publicly labeled Wegener’s theory a “fairy tale.”

The majority of geologists continued to believe in a static Earth and land bridges that somewhat mysteriously appeared and disappeared until the early to mid-1960s, when several geophysicists found paleo-magnetic evidence of continental drift. And suddenly everyone climbed on the bandwagon. Today, well more than 70 years after his death, geoscientists have finally acknowledged the power and the validity of Wegener’s basic theory, if not its finer details.

Author’s Note: As an aside, Wladimir Köppen, a highly respected biogeographer, plant physiologist, and one of the world’s great climatologists, was Wegener’s father-in-law and scientific collaborator. Wegener died in Greenland in late 1930 several days after his 50th birthday during a ferocious blizzard in which the surface temperature dropped below -60° F. He and members of his research team had been studying the effects of the ice cap on the climate of the northern latitudes around the island. As a tribute to his life-long dedication to scientific research, his body was left on the ice where it was found, marked by an enormous block of carved ice topped by a 20-foot high iron cross. Since that time, both the ice block, the iron cross, and Wegener’s body have disappeared into the glacier.

Holmes, Arthur              Without debate, Arthur Holmes (1890-1965) was one of the most creative and important geologists of the 20th Century. Shortly after Bertran Boltwood’s 1907 discovery that uranium decayed slowly to stable lead, Holmes, then an undergrad student at the Imperial College of London, was smitten by what he thought were obvious geological implications of radioactive decay and lost no time in switching majors from physics to geology. By 1911, using only analytical chemistry applied to a few mineral samples, Holmes established a framework for a new geologic time scale that proved to be uncannily accurate, considering the deficiencies of his approach since it predated the discovery of isotopes. Building on Boltwood’s pioneering research, Holmes performed the very first uranium-lead analysis of rock specifically determined for age-dating purposes. That research resulted in a date of 370 million years for a Devonian specimen.

Although only 21 years old and still an undergraduate, Holmes had embarked on a lifetime’s quest “to graduate the geological column with an ever-increasingly accurate time scale.” Two years later in 1913, at the incredible age of 23 and at that time a young graduate student who had not received the doctorate, Holmes published the first edition of what was to become a world-famous geological reference, The Age of the Earth, in which he estimated the Earth’s age at 1.6 billion years. That work propelled him to the forefront as the world’s leading authority on geochronology. His later work on radioactivity, geological time, and petrogenesis led him to a profound understanding of processes in the Earth’s interior. Consequently, he was the first prominent geoscientist to propose that incredibly slow-moving convection currents in the mantle caused continental breakup, sea-floor formation, crustal assimilation, and continental drifting. In 1929, he suggested that radioactive decay as an internal heat source might be sufficient to produce convection currents in the Earth’s mantle, confirming British geologist Osmond Fisher’s earlier proposal. His idea was based on the fact that as a substance was heated its density decreased and the hot material rose to the surface where it cooled, became denser and sank, only to rise again as it absorbed heat. That repeated heating and cooling cycle would result in a current that Holmes thought would have sufficient power to effect continental movement. Holmes suggested that thermal convection worked like a conveyor belt and that the upwelling pressure could break up continents and convection currents would then carry the broken pieces in opposite directions and eventually downward to be heated again and rise. In 1932, continuing his search for a simple dating technique, he proposed a “new key to petrogenesis” that described the principle now known as initial ratio (the ratio of a daughter isotope to a reference isotope at the time of isotopic closure). With ideas far ahead of his time, Holmes was a deep thinker and philosopher of science who was immersed from an early age in the most critical geological challenges.

However, Holmes was considered a maverick by the mainstream geological community for his persistent belief in Continental Drift Theory and was subjected to trenchant criticism that bordered on ridicule. He had the good fortune of living long enough to see the dawn of plate tectonics and the retractions of his many previous critics. In 1963, the theory of sea-floor spreading was proposed, validating his earlier theories which, by then, had almost been forgotten. In 1965, the second edition of his seminal Principles of Physical Geology was published only months before he died. In it he modestly noted that “mantle currents are no longer regarded as inadmissible.” Author’s Rant: How Holmes restrained from bashing his detractors with a club assembled from their own ignorance is beyond my understanding. Few people would have demonstrated his remarkable self-control, moderation, and charity. Today, he is justly acclaimed as one of the most important geoscientists of the 20th Century. Holmes’s life and his work offer all students of the Earth many lessons, especially for those who accept the risks of struggling against the flow of accepted wisdom but also for those who would rather swim with that current while ridiculing their more independent-minded colleagues. See absolute age, geologic time scale, and radiometric dating. For a good read on Holmes’s life, see: Cherry Lewis, The Dating Game: One Man’s Search for the Age of the Earth, Cambridge, England: Cambridge University Press; 2000.

Dietz, Robert S.             One of the first geologists in America to specialize in marine geomorphology and oceanography. Dietz (1914-1995) received a doctorate from the University of Illinois but did most of his graduate research at the Scripps Institution of Oceanography in San Diego, California, where he became one of the first geologists to specialize in marine research. After WWII, in which he served as a pilot in the U.S. Army Air Corps, Dietz organized and became the first director of the Sea Floor Studies Section at the Naval Electronics Laboratory (NEL) in San Diego where he initiated a research program in topics involving coastal and marine geomorphology, including submarine scarps, deep sea fans, and submarine canyons.

He was an early and convincing proponent of continental drift and wrote critical and incisive papers defining and contributing to a concept he was the first to identify as sea-floor spreading. At about the same time as Harry Hess was formulating his ideas about movements of oceanic crust, Dietz independently proposed a similar model in the article, “Continent and Ocean Basin Evolution by Spreading of the Seafloor,” published in 1961 in the journal Nature, which he named sea-floor spreading. Dietz’s sea-floor spreading model also broke new ground, so to speak, by assuming the sliding surface was at the base of the lithosphere, not at the base of the crust.

His highly original contributions include work with which nearly every student of geoscience is now familiar: the geomorphic evolution of continental terraces, the origin of continental slopes and margins, development of the Hawaiian swell, sedimentation in continental terraces and in the deep Pacific, and development of abrupt slope changes at the continental margins. He contributed broadly to knowledge of the geomorphology of the northwest Pacific and the Arctic basin and to a more complete understanding of turbidity-current channels.

As a graduate student Dietz had been extremely interested in lunar craters and the Kentland structure in Indiana and identified it as a meteoric impact site and initially wanted to use it as a dissertation topic. He returned to that interest during the latter years of his professional career, achieved renewed prominence by studying impact craters, both on Earth and on the Moon, arguing that those craters were common landscape features on both, an idea that was slow to be accepted by many colleagues since it smacked of what all too many thought of as the heresy of catastrophism. He was the first geoscientist to describe shattercones, identifying them as evidence of ancient meteorite impact sites. Dietz eventually described more then 130 previously unknown sites and coined the phrase astrobleme to describe impact structures created by high energy extraterrestrial objects striking the Earth, making him an enthusiastic advocate of neo-catastrophism. But perhaps best of all, he lived long enough to see most of his sea-floor spreading theories confirmed, though they had been derided as fabulist and iconoclastic by his colleagues in the 1950s and early 1960s. Find out that your ideas were right is the best way to end an argument. In 1987 after almost two years of attending numerous creationist conferences and corresponding with many creationist advocates, Dietz collaborated with scientific illustrator John C. Holden on the book, Creation/Evolution Satiricon: Creationism Bashed, a lighthearted but spirited refutation of creationist views of Earth history. Without a doubt, Robert Dietz was one of the most remarkable geologists and astrogeologists of the 20th Century.

Hess, Harry H.               American scientist (1906-1969), PhD from Princeton University, active in the fields of geophysics, marine geology, geodesy, tectono-physics, and mineralogy. He became a professor of geology at Princeton University in 1934 and remained there until his death. His specialty was the study of arced chains of islands with active volcanoes. As early as the mid- to late 1930s, through Richard M. Field at Yale, Hess became involved with Dutch geophysicist and geodesist, Felix A. Vening-Meinesz (1887-1966), who had invented a novel gravimeter that was able to function at sea since it was resistant to external disturbance, and geophysicists Maurice Ewing and Edward Bullard. Collectively, they began measuring gravity anomalies in the Caribbean and the Gulf of Mexico that demonstrated an association between negative gravity anomalies (regions characterized by lower than normal gravity) and regions where the ocean was particularly deep (what we now call trenches). Familiar with European arguments over continental drift, Vening-Meinesz proposed that convection currents might be dragging the crust downward into the denser mantle below, explaining both the ocean trenches and their associated negative gravity anomalies. Hess thought that the crust had buckled vertically as expressed on the surface as ocean trenches and in gravity measurements as negative anomalies. Borrowing a term from German geologist Erich Haarmann, he called these downwarpings in the crust, tectogenes. He thought those phenomena were downfolded portions of an orogenic belt caused by horizontal compression that had resulted from the convergence of sub-crustal convection currents. In their discussions, both Hess and his mentor Vening-Meinesz agreed that the gravity readings were signs of crustal disturbance or deformation, indicating that apparently the ocean basins were not static but were subject to active deformation, at least in certain zones.

World War II intervened in Hess’s research and he joined the Navy as an officer. During the war years Hess spent much of his time measuring the oceans with a new instrument, a Fathometer that basically outlined the ocean floor topography to the deepest points to that date, about seven miles deep. He discovered hundreds of flat-topped volcanic mountains on the Pacific floor and found them intriguing. The name he gave them was guyot, after the first geology professor at Princeton. Their tops appeared to be eroded but they were up to two kilometers under water. After WWII he continued researching guyots and mid-ocean ridges. With the discovery in 1953 of the Great Global Rift, a volcanic valley running along the mid-ocean ridges, Hess re-examined the geophysical data he had collected from the ocean floors during WWII.

Extending the ideas first developed by the English geologist Arthur Holmes in the 1930s and inspired by the work in geomagnetism being done in England by Keith Runcorn’s group at Cambridge and Patrick Blackett’s at Manchester and Imperial College, Hess re-visited the ideas he and Vening-Meinesz had developed prior to WWII. Beginning in 1960 Hess published several seminal works (the first was in a technical report to the Office of Naval Research because he was leery of sending his revolutionary ideas to one of the mainstream geoscience journals before getting feedback from colleagues) that proposed that the Earth’s crust was composed of iron-poor rock that had risen to the surface when radioactive decay heated and melted rocks in the interior of the newly condensed planet. His arguments relied on geomagnetic research by the British geophysicists and heat flow measurements by his former colleague Edward Bullard, who was then working with Scripps scientists Arthur Maxwell and Roger Revelle, that demonstrated that heat flow through the oceanic crust was greatest at the mid-ocean ridges, a finding that was consistent with rising convection currents. In his now famous 1962 article, “History of the Ocean Basins,” Hess theorized that once the planet had formed, convection currents of rising and sinking molten material were created by the continued heating of the planet’s interior. That mantle convection was subdivided into numerous separate circulating systems extending upward from the core. Where the currents rose to the surface, molten material was extruded, simultaneously building up the mid-ocean ridges and forming new oceanic crust as it spread out. According to Hess, as the magma cooled it laterally pushed the existing sea-floor away from the mid-ocean ridge, dragging the volcanic guyots into progressively deeper water as they were forced further away from the higher elevations of the ridges (see plate tectonics, history of; sea-floor spreading; and sea-floor spreading, theoretical development of). Hess’s elegant but simple theory accounted for and united several seemingly unrelated puzzles in marine geology: the youthful ocean floor, island arcs, deep sea trenches, the origin of mid-ocean ridges, the rift valley running along the mid-ocean ridge, the sinuous continuation of the ridge around the globe, and the correlation of the ridge with earthquake epicenters.

In recognition of the importance of Hess’s research, in 1966 the Geological Society of America gave him its highest award, the Penrose Medal. Also in 1966 he was elected to foreign membership in the Academia Nazionale dei Lincei of Rome, the world’s oldest academy of science, and became the first geoscientist from the Western hemisphere to receive its Feltrinelli Prize. His contributions to understanding the plate tectonic process that shapes the Earth were nothing short of remarkable. Hess’s work easily made him one of the most important geoscientists of the 20th Century.

Wilson, John Tuzo             Canadian geophysicist and geologist (1908-1993) who studied at the University of Toronto where he earned a BA with a double major in physics and geology, Cambridge University (Master’s in physics), and Princeton (PhD in geology) whose ideas in the 1960s about transform faults, permanent hot spots in the mantle, and an elaborate cycle of mountain building that included the opening and closing of ocean basins (the Wilson Cycle) were instrumental in the formulation of the theory of plate tectonics. Wilson, and other scientists, especially Robert Dietz, Harry Hess, Drummond Matthews, and Frederick Vine, were the principal architects in the early development of plate tectonics during the mid-1960s – a theory that is as vibrant and exciting today as it was when it first began to emerge from the minds of those and other geo-scientists who formed the cutting edge of plate theory.

In 1963, Wilson developed a concept crucial to the plate-tectonics theory. He suggested that the Hawaiian and other volcanic island chains may have formed due to the movement of an oceanic plate over a stationary “hot spot” in the mantle. That idea tackled head on a strong objection to plate-tectonics theory – that active volcanoes such as are found in Hawaii are located many thousands of miles from the nearest plate boundary. Hundreds of subsequent studies have proven Wilson right. But, in the early 1960s that concept was considered too cutting edge and even scientifically unacceptable that his “hot spot” manuscript was rejected by all the major international scientific journals, each of which contended that Wilson’s ideas were at complete variance with the latest seismic research findings. And that was despite Wilson’s reputation and his three-term service as President of the International Union of Geodesy and Geophysics. This manuscript ultimately was published in 1963 in a relatively obscure publication, the Canadian Journal of Physics, but later became one of the foundations of plate tectonics theory. And that’s a lesson in sheer determination for everyone.

Tuzo Wilson, in an effort to explain sea-floor fault lines, was the first to tackle the far-reaching implications of sea-floor spreading. Around the globe, researchers had noted faults or fractures perpendicular to the mid-ocean spreading ridges that cross whole oceans and break the ridges up into segments. When Wilson took up the question, the favored interpretation was that the faults were evidence of the tearing of the ocean crust from edge to edge. The ridges were assumed to have started out as continuous features that were later fragmented and offset by the faults. Wilson disagreed. Yes, the faults were evidence of crustal tearing, but only between the spreading ridge segments, segments that had always been offset. This new view suggested that active deformation is concentrated at the ridges and along their connecting faults and that the rest of the ocean crust simply drifts along, unbroken. Wilson gave the name “plate” to these large masses of moving rock. He further proposed that Earth’s surface was divided into about seven large crustal plates and several smaller ones.

Wilson’s ideas about oceanic faults and plates were easily tested by the emerging earthquake location data set and Lynn Sykes, working at Lamont Geological Observatory, was quick to try this test by examining rock movement in ten earthquakes along two mid-ocean ridges and found Wilson’s predictions to be borne out in each case. Sykes found that oceanic earthquakes were, indeed, concentrated along the mid-ocean ridges and their connecting faults, and that the interiors of the oceanic plates were nearly aseismic, or earthquake-free. See J. Tuzo Wilson, “A New Class of Faults and Their Bearing on Continental Drift,” Nature, vol. 207, pp. 343-347, 1965; reprinted in Allan Cox, Plate Tectonics and Geomagnetic Reversals: Readings. San Francisco: W. H. Freeman, 1973; and J. Tuzo Wilson, “Did the Atlantic Close and then Re-Open?” Nature, vol. 211, no. 5050, pp. 676-681, 1966, an interesting treatment is contained in Lynn S. Fichter and David J. Poche, Ancient Environments and the Interpretation of Geologic History, 3rd edition, New York: Prentice Hall, 2001.