J.Tuzo Wilson

DEAR DR BELOUSSOV:

It is kind of you to address an open letter to me. I agree with much of what you say and a few Years ago I would have agreed with more. On the other hand the existence of important differences make me grateful to the editor of Geotimes for this opportunity to reply. May I assure you that these differences in no way diminish my regard for the great contributions you have made in promoting international coöperation as a member of the Special Committee for the International Geophysical Year, as president at the Berkeley meetings of the International Union of Geodesy & Geophysics in 1963 and as chairman of the Upper Mantle Committee.

I shall pass over some minor divergences in point of view in order to come to the fundamental argument between us. lt is that you continue to believe that continents and ocean basins have always been fixed, whereas 9 years ago I was converted to the, view that extensive horizontal movements have occurred. Indeed, I now hold that the lithosphere has repeatedly been broken into plates which have travelled extensively relative to one another and that this has gone on throughout much of geologic time and not only since the late Palaeozoic as Wegener suggested.

In spite of this fundamental difference, I still accept much of what you say. I agree that most geological observations made on continents are accurate, important and not to be disregarded. I agree that most of the evidence for continental drift which you cite has been discussed for a long time with inconclusive results. In spite of the efforts of such men as Taylor (1910), Baker (1911), Wegener (1912), du Toit (1937) and more recently Carey (1958), Runcorn (1962), Blackett ( 1965), and Bullard ( 1965) you can justify your statement that 'the contours of the coasts, paleoclimatic data, structural similarities etc. can always have another interpretation' on the grounds that these arguments converted only a few to believe in drift. For many years after they had been advanced the great majority of geologists and geophysicists rejected them, (R. T. Chambertín 1928 and Jeffreys 1959).

It is also true that arguments based upon the postulated existence or non-existence of mechanisms may be of doubtful value. Thus I agree that the arguments YOU mention would not by themselves have justified a radical revolution. .

The chief difference between us is not about what you say, but arises from what you. have omitted to say. Your arguments would have had some validity a few years ago, but it seems to me that they have now been superseded. It astonishes me that you almost completely ignore the tremendous recent discoveries. It is they, not the old topics you mention, which have changed so many opinions, which have inspired a revolution in the earth sciences, and which have produced the beginnings of an elegant and precise new explanation of the Earth's behavior (Morgan 1968; Le Pichon 1968, and Isacks, Oliver & Sykes 1968).

The new arguments which you dismiss or ignore, but which I consider conclusive, fall into three groups that may be classed under the headings of sea-floor spreading, paleomagnetism and seismology.

The notion that ocean basins have spread from mid-ocean ridges was advanced by Holmes (1931) and Hills (1947) and used in both editions of Holmes' textbook. lt received impetus from the discovery by Ewing & Heezen (1957) of the continuity of mid-ocean ridge system. This led to the greatly improved views on spreading of Hess (1962) and Dietz (1961). Evidence supporting ¡t has come from, many directions.

lt has been observed that islands and cores tend to increase in age from the crests of mid-ocean ridges towards the margins of ocean basins (Wilson 1963a, Funnell 1966, Burcke et al 1967). This supports the idea of spreading from the mid-ocean ridges as does Ewing & Ewing's (1967) observation that sediments increase in thickness in the same direction. The discovery and exploration of fracture zones by the U. S. Coast & Geodetic Survey, H. W. Menard (1964), Heezen et al. ( 1964) and others led to the hypothesis that growing oceans should be crossed by transform faults which should differ from transcurrent faults in three respects: ( 1 ) they should not enter the bounding continents, (2) their seismicity should be confined to the axial line and its offsets, (3) their directions of motion should be in the reverse directions to those for simple offsets. The demonstration that many fracture zones have these properties has gone far to prove that ocean basins are indeed spreading (Wilson 1965a, Sykes 1967). I should like to take this opportunity of acknowledging that my own views on ocean floors have been much helped by the splendid bathymetric charts published in the Soviet Union, notably by Udintsev (1964).

You dismiss the proposal by Vine & Matthews (1963) that the pattern of magnetic anomalies over mid-ocean ridges supports ocean-floor spreading. I consider that even the earliest evidence for regular patterns of magnetic anomalies on the ocean floor was clear (Raff & Mason 1961) and I cannot believe that ¡t would he true now to dismiss the vast and regular patterns set forth by Vine (1966), Heírtzler et al. (1968) and Deminitskaya & Karisik (1966) as 'rather irregularly scattered patches'. You say nothing of the supporting evidence for paleomagnetic, reversals by Cox, Dalrymple & Doell (1967), McDougall & Chamalaun (1966) and, in cores, by Opdyke et al. (1966).

The second group, of modem discoveries that you also dismiss briefly are concerned with paleomagnetism. Some of the contradictions and difficulties you mention may be valid, but others are natural in the development of a new subject. What is more important is the much greater body of consistent observations. Those on young rocks agree with the present pattern of continents while those on older rocks suggest systematic changes in that pattern (Irving 1964; Krapotkin in press). No one has done more to show that the Earth's field has long been dipolar and hence to remove one source of doubt than your compatriots Khramov et al. (1966).

A third modem development has been published only since your letter, Isacks, Oliver & Sykes (1968) say that modem views on drift can explain the distribution, mechanism, direction of motion of earthquakes with a detail that was quite lacking before.

I think that you should answer the grave objections to fixed continents which these three modern lines of evidence pose before you reject all the many possible hypotheses of moving continents. By the same token I am glad to try to reply to the eight specific questions your letter addressed to me, for I think ¡t is possible to fit your observations into an appropriate version of continental drift. My answers:

(a) The explanation suggested by Hess (1962) seems excellent to me.

(b) I believe that except for thicker sediments the floor of the Sea of Okhotsk is the same as that of the adjacent Pacific because the Kuril arc is younger than the floors. The Caribbean is a tongue of the Pacific (Wilson 1966). The Black Sea, Eke the Mediterranean, is a remnant of the closing Tethys Ocean (Le Pichon Wilson in press). Mie Sea of Japan may he older and more complicated and I cannot yet explain it

(c) The ocean floor ¡a deformed into deep trenches at the edge of continents where plates of the lithosphere override one another (Isacks, Olíver & Sykes 1968).

(d) Your confusion arises from adhering to the outmoded views of Wegener. Continents are no longer regarded as rafts moving through a plastic ocean floor. The whole lithosphere, at least 50 km thick, is brittle and broken into plates of which continents form incidental parts. When viewed in this way your problems about the Americas do not arise.

The question of how the mid-ocean ridges which encircle Africa (and Antarctica) can expand has puzzled many until they have realized that upward and outward flow beneath the ridges is possible íf the ridges themselves are moving their positions outwards (Wilson 1965b).

(e) If flow occurs it is in the asthenosphere or low. velocity layer of seismology lying between depths of 50 and a few hundred kilometers (Anderson 1967). The other problems you raise cover some of the main problems of geology. Even if they have not yet been fully explained by the new ideas, they were certainly never fully comprehended by the old, and the problems are vast and would take too long to discuss here. Gorshkov and Eaton & Murata (1960) have discussed evidence for sources of magmas. I believe that: in the oceans some volcanoes may become detached from their roots (Wilson 1963b), but this does not seem to happen under continents.

(f) Although major geological phenomena are recurrent, the problem of whether cycles are regular and universal is still debated. If drift has depended upon the fracture and relative movement of plates of the lithosphere, at any one place it would probably appear to be intermittent because it would depend upon the way in which the lithosphere had broken and moved. Ocean basins have, I believe, repeatedly opened, grown and closed again (Wilson in press). The fife histories of al] ocean basins might be generally similar and hence give the impression of tectonic cycles.

(g) Schuiling (1966) has given one explanation of why heat flow is much the same over ocean and continents. Knopoff, Von Herzen and your own distinguished colleague E. A. Lubimova have discussed this problem at length in a recent book (Gaskell 1967).

(h) This again raises major problems, but one explanation of why evidence of high temperatures can be found in places where currents have descended could he that at these places one plate of the lithosphere has been overridden by another, pressed down, heated, and then subsequently risen isostatically from great depths.

In conclusion, those of us who hold the new point of view do not wish to discredit or discard the old data. lf we hold that it was insufficient, it is because we want to draw attention to data of the new kinds. Your lack of reference to the new shows how necessary this is, although at the recent International Geological Congress some of your colleagues assured me that 80 per cent of Soviet earth scientists have accepted continental drift (for example, Voronov 1968 and Krapotkin in press). What we want to change is not the data, but the frame of reference or the way of looking at data. (If two groups of scientists both studied whirlpools, and one group held that the water in them did ~ move they would never understand whirlpools no matter how much data they collected. The other group, which admitted that the water was moving, could understand the nature of whirlpools with little data.)

I hold that the trouble with the earth sciences (geology, geophysics and geochemistry alike) and the reason they have not progressed as they might has been not lack of or errors in data of traditional kinds, but a lack of the new kinds of information and an utterly wrong way of looking at the Earth. lf indeed the Earth is, in its own slow way, a very dynamic body and we have regarded it as essentially static, we need to discard most of our old theories and books and start again with a new viewpoint and a new science.

I believe that what is happening in earth sciences la similar to what happened in chemistry about A.D. 1800, in biology when evolution was introduced, in physics when classical views were replaced by modern. It’s not new data, but a change in outlook that marks a scientific revolution, as T. S. Kuhn (1964) has so elegantly pointed out. If a scientific revolution la In progress in the earth sciences it provides us all with an exciting opportunity, the prospect of a great revival¡, and I think we should embrace the change and expect the whole study of the Earth to move rapidly forward.

I believe this revolution will unite branches formerly fragmented and that the new unified science of a dynamic Earth deserves a new name---geonomy.

Thank you, again for this opportunity to make my views clear. Because it was my ideas which you singled out for attack, they have received more attention in this reply than they would otherwise deserve.

Recent publications:

P. M. S. Blackett, Edward C. Bullard & S. K. Runcorn, editors, A symposium on continental drift: Phil. Trans. Roya¡ Soc. London, v. A258, p. 1.323 (1965).

Gerard Piel, editor, Gondwanaland revisited: new evidence for continental drift, Proceedings of the American Philosophical Society, v. 112, n. 5, (1968).

E. Takeuchi, S. Uyeda & H. Kanarnori, Debate about the Earth, Freeman Cooper & Co., San Francisco, 253 p~ (1967).

T. 5 ' Kuhn, The structure of scientific revolutions, University Of Chicago Press, 172 p. (1964).In preparation or in press

Marshall Kay, editor, Symposium on the North Atlantic area, Ajaer. Assoc, Petrol, Geol.

1. Tuzo Wilson, editor, Symposium on continental drift in the South Atlantic region, Unesco, Paris.