John Milsom was surprised to find a paper on sea-floor magnetic stripes published in 1958. Here he unravels the reasons why these fundamental data, which proved so important for plate tectonics, went unnoticed for so long. It is unsettling when a “fact” long accepted turns out not to be a fact at all. For 50 years I had believed that the oceanic magnetic “stripes” that provided the clinching evidence for plate tectonics first entered the public domain in 1961, in back-to-back papers authored by Ron Mason and Arthur Raff (Mason & Raff 1961, Raff & Mason 1961). I was wrong. It was in 1958, and not in 1961, that the stripes first appeared in the geological literature and, of particular interest to members of the RAS, it was in the first volume of the Society's Geophysical Journal (then known as the GJRAS, now Geophysical Journal International) that they were presented to the world (Mason 1958). But I was not alone in my ignorance. Lawrence Morley (2001), who would have preceded Vine and Matthews (1963) with an explanation of the stripes if reviewers had been kinder, and who should have known the true facts if anyone did, stated firmly that “Raff and Mason's zebra map first appeared in August 1961”, and similar comments are the norm in the literature. Fred Vine would have found the 1958 paper during the literature search that began his PhD, but that was in 1962. When it was published he was still at school. It seems, therefore, that the speedy transition from problem to solution that I had imagined was actually a leisurely progression including a three-year interval during which nothing much seems to have happened. At the heart of the delay was Mason's character (figure 1), which I came to know well 10 years later. He was my PhD supervisor between 1968 and 1971, and my head of department during the subsequent years when I was teaching at London's Imperial College. In unravelling his story I have relied heavily on what he and others wrote in Naomi Oreskes' collection of the memoirs of the more long-lived of the key figures (Oreskes, 2001), and also on the very personal memoirs of Bill Menard, who sadly was not among them (Menard 1986). 1 View largeDownload slide The scientific staff of the R/V Spencer F. Baird (Capricorn expedition). Rather typically, Ron Mason is in neither the first or the second row, but forms a row of his own between them. (Helen Raitt Papers. SMC 19. Special Collections & Archives, UC San Diego Library) 1 View largeDownload slide The scientific staff of the R/V Spencer F. Baird (Capricorn expedition). Rather typically, Ron Mason is in neither the first or the second row, but forms a row of his own between them. (Helen Raitt Papers. SMC 19. Special Collections & Archives, UC San Diego Library) The Capricorn expedition The story begins in 1952 with Mason, already a lecturer at Imperial but on sabbatical at the California Institute of Technology, attending a meeting at the Scripps Institution of Oceanography. A chance remark of his, overheard by Robert Revelle, head of Scripps, led to an invitation to make magnetic measurements on the Capricorn cruise to the South Pacific. Scripps had no suitable instrument, but one was borrowed from Lamont. Also on Capricorn was Arthur Raff, who was to be Mason's partner in the investigations that were to follow, but who at the time was busy improving the Scripps hydrophones. The two did not overlap. Raff left the ship in Samoa and Mason joined it in Suva. The magnetometer was towed almost continuously and the magnetic field was recorded along almost 7800 nautical miles of track. The Tonga Trench was crossed twice and there were special surveys around half-a-dozen atolls, islands and seamounts. The system used was only briefly described in the preliminary cruise report (Revelle et al. 1953), without indicating how the results were recorded, but Helen Raitt, the first woman to take part in a US oceanographic expedition, has given us a clue. Her presence on board was unofficial and almost accidental, but her account of her experiences (Raitt 1956) provides a vivid picture of life on those early post-war expeditions. She said: “Ronald Mason, our Englishman … usually turns up in the lab about midnight to work on his magnetometer records. He is a lone wolf, working late at night when there is more space on which to spread out a twenty-three-foot-long record,” (Raitt 1956). This sort of pen-and-ink record was already standard in airborne surveys at the time. As the magnetometer had been adapted from airborne use, its use at sea was to be expected, but the confirmation is welcome. Magnetic reversals The magnetic work carried out on the Capricorn expedition amounted to little more than proof of concept. More could be achieved only if track-lines were sufficiently close together for anomalies to be correlated between lines, and usually achieving this was incompatible with some of the things that other scientists wanted to do. It was not until 1955 that an opportunity to measure magnetic field on a regular grid presented itself and by that time Mason had been on another cruise and had done some very different but potentially important work with Raff. Operating some 400 km southwest of the tip of Baja California, they collected cores up to almost 10 m long from the red clays that floored the ocean. Mason took the samples back to London to measure magnetic directions, and in each core he found a sequence of alternating normal and reverse magnetizations. Correlation between the cores was difficult because their uppermost sections were often missing, but Mason became convinced that he had good evidence in favour of the then controversial idea of frequent reversals of the Earth's magnetic field. He circulated a manuscript to that effect among his colleagues, but was told “he would look like a fool” if he published it, so he didn't (Menard 1986 p71). In his own account (Mason 2001), neither this cruise nor its outcome is mentioned, but the very negative way in which his ideas were received may have had a lasting influence. When, in 1968, he inherited me as a PhD student, almost his only comment was that New Guinea was a risky place to study because there was a lot of new work being done there, and I might be proved wrong in a few years. Could it have been his early put-down that produced this ultra-cautious attitude? Menard also remarked: “If there was one subject on Ron Mason's mind in the next few years it was surely the reversal of the Earth's magnetic field.” If so, it certainly didn't show. The one thing Mason never suggested in anything he published during that period was that adjacent stripes might be magnetized in opposite directions. It was an idea that, 40 years later, he “kicked himself” for not having thought of (Mason 2001). The Pioneer surveys After measuring his cores in London, Mason returned to Scripps in early 1955, at just the time when the US Navy had decided to map the floor of the Pacific Ocean out to 300 nautical miles from the coast of the United States. It was to be a very detailed survey, with a line spacing of just 5 nautical miles made possible by the recently developed Loran-C navigation system, which was installed in the USCGS Pioneer. Menard suggested to the Navy that they tow a magnetometer during the survey, but the response was less than enthusiastic. The US Geological Survey, when consulted, said it would be a waste of money and the Office of Naval Research refused its support. In the end, the funding was found by Roger Revelle from his small discretionary budget at Scripps, but only after the first of the month-long cruises (which continued through to October 1956) was under way. The Navy's lack of enthusiasm was not, however, entirely a bad thing. They regarded the bathymetry as secret, but allowed the magnetic results to be published. At first, it seemed that the sceptics were right, because there seemed to be far too many anomalies for sensible mapping. It was not long, however, before it became obvious that the E–W ship tracks were cutting across a series of highly elongated magnetic features trending roughly N–S. This would have been so clear even in the unprocessed data that the point could have been made by just publishing profiles on a map base, but to Mason such a “quick and dirty” presentation would have been anathema. He was determined to use quantitative methods to separate the geologically related magnetic anomalies from the much larger Earth's field background, “by overlaying my contour map on the map of the Earth's magnetic field published by the Hydrographic Office, and subtracting the one from the other graphically. This rather tedious procedure greatly simplified the original map,” (Mason 2001). To Menard, who saw Mason at work back at Scripps, the process of plotting the thousands of magnetic observations appeared to be not merely tedious but “vexingly tedious” but he described a rather different procedure, with Mason calculating moving averages of the readings and then subtracting these from the individual observations. Not only did the work seem endless, but it also concealed the fact that the anomalies were symmetrical north of the Mendocino escarpment. The differences between Menard's and Mason's accounts cannot now be resolved with any certainty, but it is possible that both are true. Menard saw Mason only at Scripps, but maps of a sort were also produced at sea, and Mason's description may relate only to these. Once ashore, he may have decided that this was not good enough and adopted what he believed to be a more rigorous approach. It may have been designed to minimize the effects of instrumental drift, but that highlights another oddity, because by 1955 the techniques for processing aeromagnetic data were already established. For each flight line, a magnetic baseline was estimated and lines were drawn on the charts parallel to it at the selected contour interval. Only the points where these lines cut the magnetic profiles were plotted on the map, and contouring was made very simple. Victor Vacquier, who knew all about airborne surveys, was a frequent visitor to Scripps and could have told Mason about this much quicker method. Either he never did or Mason, as he so often did, preferred to do things his own way. The path to sea-floor spreading As the magnetic data poured in and Mason continued his processing, his colleagues grew impatient. By 1958, Revelle needed to justify the use of his funds and, in order to galvanize Mason into action, Menard and Vacquier published a short note about the stripes in the Office of Naval Research Review. It worked. Mason published in the GJRAS by the end of the year, but using only the data from the first three cruises (figure 2). 2 View largeDownload slide The first published map of the magnetic stripes, from Mason (1958; figure 2). The linearity is clear, as is the offset at the Murray Fracture Zone. 2 View largeDownload slide The first published map of the magnetic stripes, from Mason (1958; figure 2). The linearity is clear, as is the offset at the Murray Fracture Zone. It should have been enough. Only a few years previously, Menard and Bob Dietz had, to general astonishment, discovered the spectacular oceanic fracture zones that cut the East Pacific Rise. The Murray Fracture Zone, which dramatically displaces the magnetic stripes in figure 2, had been one of the first to be found. What even the 1958 map was showing was both unexpected and extraordinary, and clearly part of the same story as the fracture zones. It must have been clear to anyone who looked at it that an explanation was required. By comparison, the Vine–Matthews (1963) paper that ultimately provided that explanation seems very low-key and its important conclusions were quite well concealed in the text. Yet that paper revolutionized geology while Mason's paper had almost no impact. The reasons for that can be found in the character both of Mason himself and of the institute within which he worked. One reason for the publication delay was that Mason allowed himself to be distracted. With the Pioneer surveys only half complete, he left Raff, the instrument man, in charge and took on the management of three magnetic observatories on islands in the equatorial Pacific. The timing of this programme was dictated by the International Geophysical Year, but fortuitously there were several US and British atomic bomb tests while the observatories were “live”, and unexpectedly large magnetic effects were recorded. Mason wrote about these for Nature (Mason & Vitousek 1959). His absences in the Pacific may explain why the northern stripes were reported in a separate paper for which Raff was first author; in the pages of the Geological Society of America BulletinRaff and Mason (1961) follows on immediately from Mason and Raff (1961). It is shorter and contains no quantitative interpretation, but the magnetic anomalies it presents are even more spectacular than those further south and, in what is described as a “key map”, are presented in a more striking fashion. The areas where the magnetic field is above the baseline value are shaded black and those where it is below are left white, and it is this map that has since been most widely reproduced. It is somehow typical of Mason that, in the equivalent map where he was first author, the positive anomalies are shaded grey. It is also true that for much of the time when he was not out in the Pacific, Mason was in another wrong place. At the time there were really only three institutions that were both open to ideas involving continental drift and contained the critical mass of scientists meeting on a regular basis and able to bounce ideas around over the coffee cups. Scripps was one, Princeton was another and Cambridge the third. Mason's home base was Imperial College's Royal School of Mines. It had a distinctive, and proud, orientation towards applied geology and geophysics, but was not a place much interested in ideas about global tectonics. It was not likely that anyone there would seek him out to discuss them; it was in any case often unclear to his colleagues whether he was in South Kensington or California. During the 1961–62 academic year, when I was doing the diploma course at Imperial, I cannot recall ever having seen him. When at Scripps he would have been in contact with a critical mass but, although anyone less vulpine than Mason would be hard to imagine, Raitt was at least partly right in describing him as a “lone wolf”. He was almost chronically shy and I cannot help feeling that his preference on Pioneer for working at night was not entirely dictated by the extra space available. The choice Why then, in 1958, did Mason choose to publish in the GJRAS? Now as Geophysical Journal International, it is a high-impact publication and would be an uncontroversial choice even though, given the location of the Pioneer surveys and the nature of their sponsors, a US journal would have been more logical. But in 1958 it was in its first year of publication, and few of the scientists interested in the geology of the ocean floor would even have been aware of its existence. Ten years later, as I well remember, if a Fellow of the Geological Society wanted to look at it, the Geological Society librarian would ring up the Royal Astronomical Society librarian and the Fellow in question would then cross the courtyard of Burlington House and would be admitted, with some ceremony, to the rooms of the sister society. The GJRAS might possibly have offered a speedier route to publication than some more established journals, but in those days publication delays were much less than they are today. Vine and Matthews (1963) submitted to Nature in late June or early July 1963 and the paper was published in September of the same year (Vine 2001). That was unusually quick, but Mason and Raff (1961) was published a little over a year after submission and may have been delayed so that it could be published alongside Raff and Mason (1961), in print only eight months after submission. Then as now, individual reviewers could hold things up, but no reviewer would have hesitated long before recommending publication of such remarkable new data. Although there may at the time have been RAS members actively seeking contributions for the new venture from colleagues in Imperial, it is hard not to conclude that the GJRAS was chosen at least partly because it was obscure. For someone who was being pressured to publish but did not think he was actually ready to do so, it might have seemed an ideal choice. The six-year gap between the discovery of the magnetic stripes and their publication in a widely read journal could have allowed those “in the know” to come up with an explanation long before Vine, Matthews and Morley. In Morley's case the revelation came when he, having already been fascinated by the magnetic stripes (particularly remarkable to someone used, as he was, to looking at continental magnetic anomalies), encountered sea-floor spreading in the paper by Bob Dietz (1961). He needed no additional data (Morley 2001). Harry Hess had been circulating his version of sea-floor spreading informally around Scripps and the US Navy since 1959, and within the same circle there had been knowledge of the stripes since 1956. Why did no one make the connection that came so easily to Morley? In Mason's case the answer is simple. He revelled in the minutiae of calculations and wanted to present maps that were as accurate as possible, and he wanted to discover the limitations on the shapes of the bodies that could produce such features. And he had a positive aversion to publishing anything that was the least bit speculative. Not only Mason but also Menard later said that they “kicked themselves” for not having seen the answer that, with hindsight, seems so obvious (Menard 2001). But the oceanographers of the day were overwhelmed by the flood of data coming from frequent cruises, and few scientists want to work on someone else's data when they have more than enough of their own. Crucially, also, the stripes posed local as well as global questions. They revealed offsets of sometimes hundreds of kilometres across the newly discovered fracture zones, yet these zones ran at high angles to the coast and where they should have come ashore they seemed to have little or no effect on the geology. From 1958, Vacquier extended the Raff–Mason coverage and discovered even greater offsets at the Mendocino fracture, a result he published alongside those of Mason and Raff (Vacquier et al. 1961). During the crucial years, it was the puzzle of what happened to those offsets at the coast that obsessed the oceanographers of the western US seaboard. Why the stripes were there at all must have seemed much less important. REFERENCES Dietz R S 1961 Nature 190 854 CrossRef Search ADS Mason R G 1958 Geophys. J. Roy. Astron. Soc. 1 320 Mason R G 2001 Stripes on the sea floor in Oreskes 2001 Mason R G & Raff A D 1961 Geol. Soc. America Bull. 72 1259 CrossRef Search ADS Mason R G & Vitousek M 1959 Nature 185 52 CrossRef Search ADS Menard H W 1986 The Ocean of Truth ( Princeton University Press, Princeton) Google Scholar CrossRef Search ADS Morley L W 2001 The zebra pattern in Oreskes 2001 Oreskes N (ed.) 2001 Plate Tectonics: an Insider's History of the Modern Theory of the Earth ( Westview Press, Boulder) Raff A D & Mason R G 1961 Geol. Soc. America Bull. 72 1267 CrossRef Search ADS Raitt H H 1956 Exploring the Deep Pacific ( W W Norton, New York) Revelle Ret al. 1953 Shipboard Report, Capricorn Expedition, SIO53-15, 26 December 1952 – 21 February 1953 (Scripps Institution of Oceanography, La Jolla) Vacquier Vet al. 1961 Geol. Soc. America Bull. 72 1251 CrossRef Search ADS Vine F J 2001 Reversals of fortune in Oreskes 2001 Vine F J & Matthews D H 1963 Nature 199 947 CrossRef Search ADS © 2018 Royal Astronomical Society
Astronomy & Geophysics – Oxford University Press
Published: Apr 1, 2018
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