revolution in the Earth sciences

In recent years the hypothesis of conlinental drift has become accepted by more earth scientists. Indeed ` many now believe that the hypothesis has attained the status of a theory. Further, as Dr Wilson explains in the next few pages, the implications for geology are far greater than a question of whether the continents were once a single mass.

This article was first presented at the 1967 meeting of the Canadian institute of Mining & Metallurgy, held in Ottawa. Then it was printed in the February 1968 issue of the Canadian Mining & Metallurgical Bulletin, and its appearance there led to the open letter by V. V. Beloussov that begins on page 17. In order to provide context for that letter, Dr Wilson and the editor of the Bulletin have given permission to reprint this article in Geotimes. Together with Dr Wilson's reply, they are published here as a debate about the Earth.

A any time, it is a pleasure to me to be invited to address the Canadian Institute of Mining & Metallurgy because it represents an industry and men with whom 1 have been happily, if peripherally, associated continuously for 40 years. is time it is a particular pleasure because I believe that an important subject has arisen which 1 propose to discuss.

This is a major discovery in the earth sciences, first fully revealed in the winter of 1966-67, but already widely accepted, The basis of this revolution, for it is no less, is that measurements of 3 different features of the Earth all change in exactly the same ratios. These ratios are the same in all parts of the world. The results from one set are thus being used to make precise numerical predictions about all the sets in all parts of the world. No such accurate correlations and predictions have ever been found before in geology or area[ geophysics. The whole subject of earth science 1135 thereby been radically altered.

The first of these measurements is that of the direction of magnetic polarity in lava flows. When piles of young lavas are examined with the aid of a pocket compass, it is noted that some flows are magnetized in the direction of the earth's field and some in the reverse direction (figure 1). By accurately dating enough flows, a time scale of the dates of reversals has been established. During the past 4 million years, of reversals have occurred synchronously all over the world (Cox, DaIrymple & Doell 1967, McDougall & Chamalaun 1966). It appears that the scale can be extended back to Precambrian times (McMahon & Strangway 1967). This time scale is the first of the 3 identical ratios.

The second group of measurements is that of the widths of successive strips of magnetic anomalies measured over ocean basins.

In 1956, Heezen & Ewing (1963) suggested that a World-encircling system of mid-ocean ridges exists. Their colleagues soon showed that magnetic anomalies occur in patterns of strips parallel to the crest of these ridges. Vine & Matthews (1963) predicted, and Vine & Wilson (1965) demonstrated, that the widths of successive anomalies were the same as the times between successive reversals of the earth's magnetic field. Heirtzier et al. (1966) and Vine (1966) have shown that, although the absolute widths vary in different places, the ratio of the widths is constant everywhere. This is the second of the 3 identical ratios.

The third group of measurements has been made by Opdyke & colleagues (1966) on deep-sea cores. They discovered that the directions of the feeble magnetization of samples taken at intervals along a deep-sea core could be measured. This magnetization is either parallel to the present field or is exactly reversed. The depths at which successive reversals take place is in a constant ratio for all cores. This is the third of the identical ratios.

The essence of the new revolution lies in this identity of the ratios of 3 independent groups of measurements. The proved coincidences are already t- great to be due to chance, and are all the more remarkable because one measurement is of time in millions of years, one is of horizontal distance in hundreds of kilometers and one is of vertical distance in centimeters.

The only explanation proposed for Opclyke's discovery is that the Earth's magnetic field is reversing and imprinting the sediments as they are uniformly deposited on the sea floor.

If the Earth's field is reversing in a known time scale and that scale reappears in distances, the relationship must take the form of a velocity. This suggests that the ocean floor is being generated along mid-ocean ridges, that it is being magnetically imprinted as it forms, and that it is being carried away from the ridges at uniform velocities. This is the theory advanced by Vine & Matthews (1963) and independently by Morley & Latochelle (1964). It is a development of the convection current hypothesis of Holmes (1928-29), as modified by Hess (1962), and likened by Dietz (1966) to a system of conveyor belts carrying the ocean floors about.

What distinguishes this theory from all past hypotheses is its precision. For example, its application to a magnetic map of the sea floor off Vancouver Island gives the following interpretation for one point chosen at random. At ]at. 47º15' N and long. 130* W, the sea floor is calculated to be moving away from the United States coast in a N 72' W direction at a rate of 6 cm per year. The rate has been steady for several million years, and the rock samples dredged from the vicinity should have been erupted between 2.0 and 2.5 million years ago and should have an average polarity exactly opposite to the present direction of the Earth's field. Ibis information was read from plate 1 in Raff & Mason (1961).

As magnetic surveys are extended, it seems likely that it will be possible to make accurate statements, such as the above, for any point on the ocean floors. Such forecasts can be checked, and this is being done. So far, the theory is proving satisfactory; if this continues, earth science will have entered a new era. The mechanism which causes the surface to move about is considered to be upwelling and outward flow from mid-ocean ridges (figure 2)

. By this process, large segments of the surface layers of the Earth are spread apart. They appear to be carried about at rates of a few centimeters a year by currents in the plastic white-hot mantle. Estimates based upon meltingpoint curves, isostatic rebound after ice-sheet melting and the propagation of seismic waves all agree that this plastic asthenosphere begins at a depth of about 50 km. Above it, the cooler and brittle lithosphere includes some of the uppermost mantle and all of the crust except deep roots of mountains (figure 3).

Upwelling and extension in some places is matched elsewhere by downward flow and compression, These segments of the lithosphere are forced together, one side over-riding the other and forcing it down to be reabsorbed under young mountains and beneath deep ocean trenches, such as exist off Chile, Japan or the Aleutians (Coats 1961).

This theory is one form of continental drift, but it is not the same as Wegener's version, for he visualized the continents as rafts moving through the ocean floors; the present concept visualizes the continents as being carried about along with ocean floor like logs frozen in ice. Elsasser (1966), Orowan (1964) and Tozer (1965) have examined this theory and find convection in a shallow layer to be physically acceptable.

The theory also explains many other observations favoring drift. These include paleoclimatic and paleomagnetic evidence; the excellent fit of the two sides of the Atlantic Ocean; the increasing age of islands and cores away from mid-ocean ridges; the apparent youth of all oceans; the new class of transform faults proposed to fit the geometry of a spreading or absorbed crust (Wilson 1965); the demonstration by Sykes (1967) that earthquakes on the mid-ocean ridge do have the direction of motion required by that theory., and other reasons summarized by Blackett, Bullard & Runcorn (1965), Runcorn (1962) and Munyan (1964).

effect on earth science

It must be obvious that the discovery of a series of precise, worldwide coincidences between different measurements will have a great effect upon earth science. To understand what this may be, consider the manner of progress in any science. There are 4 stages. The collection of data, the discovery of a precise theory, its use to make forecasts, and the checking of these predictions. Repetition of the cycle often leads to improved theories.

The difficulty about earth science has been that because the Earth is so complex and has to be studied in so much detail, the science has never progressed beyond the first stage. Geologists and solid-earth geophysicists amass data, but this has been of limited use because of the lack of any good theories upon which to base predictions- Prospectors are very well aware of the need to make predictions about the occurrence of ore and the difficulty of doing this.

Because the data which they had w" inadequate and failed to lead to any sound theories, the very idea of prediction, which is the powerful essence of the scientific method, fell into disrepute among geologists. Instead, they quite rightly tried to improve their observations and techniques. This they have preferred to do by making more precise measurements in their customary fields (paleontology, mineralogy, petrology, geochemistry, structural geology, geomorphology, etc.) rather than by studying other fields. In particular, most geophysical subjects have traditionally been studied by physicists. Most members of both groups have been so absorbed in techniques and data collection that the .search for principles has been neglected. Neither group found satisfactory theories of the Earth's behavior. Geologists' concepts applied to the real Earth, but were vague; geophysicists' ideas were more precise, but, because of their usual lack of knowledge of geology, they were applied to models too simple to bear much resemblance to the Earth.

The development of the present revolutionary theory has depended upon the contributions of both groups. These include geologists from all parts of the world, too numerous to mention, but especially those who have recently studied the petrology of ocean islands and floors, geochemists who have provided useful chemical guides to the probable nature of the Earth's interior and physicists who have devised instruments for studying the sea floor and for making new physical measurements of the Earth's interior and of the age and history of rocks.

However, it seems fair to suggest that the men who have most clearly understood what was happening and who have done most to produce this revolution have been geologists with two characteristics in common: a broad training, including an unusually good grasp of physics, and an interest in worldwide problems rather than small areas. This description applies, I believe, to such men as Holmes, Du Toit, Cirey, Hess, Heezen, Menard, Dietz, Vine, Matthews, Irving, MorIey, Doell, and McDougall. Wegener, Vening Meinesz, Bullard, and Runcorn are like-minded physicists.

As so often happens when something really new is discovered in science, the establishment, if we may so describe those larger institutions most closely concerned with the subject, had little to do with it. The petroleum and mining industries paid little attention to the idea of continental drift. The majority of the members of geological surveys and departments of geology were not expecting any such revolution. All these organizations were concentrating upon limited objectives. They were so absorbed in improving techniques, in amassing data and in planning computer codes by which to store the information that they forgot that other sciences have simplified their problems by discovering principles. Was not Tycho Brahe followed by Kepler and Newton?

The isolation in which some scientists live is well illustrated by a letter 1 received on March 14, 1967, from the director of a distinguished geological survey, which read 'The opinion of the National Committee is that the subject of continental drift, attractive and stimulating as it is, is not of priority interest to geologists in ...

In large measure, the revolution can be said to have come about because of defense spending, which Provided, for the first time, abundant knowledge of hidden places on the ocean floors, of the Moon and Mars, and of the Earth's interior (through new seismic arrays built to detect atomic bomb explosions). These discoveries opened men's minds to new possibilities.

This outlook promises well for the future for the two following reasons. Science, like clothing, moves from one fashion to another. Earth science is not forever destined to be a poor relation. A century ago, geology was the leading science. The names of Sir William Logan, Sterry Hunt and Sir William, Dawson remind us of how true that was in Canada. Geology did not decline, but the faster rise of organic chemistry, engineering, atomic physics, molecular biology, electronics, computers and other sciences eclipsed it However, these in turn lose their freshness and there is no reason why earth science, having made an important breakthrough, should not again rise to preëminence.

The other reason is that one discovery often leads to others. The excitement in earth science today lies in new ideas and the search for powerful new principles-no longer are we limited to the blind collection of better data.

effect on universities

It is well known that the teaching of earth science in universities and schools is in a state of flux. A very few departments teach combined courses in geology, geophysics and geochemistry with a suitable measure of math, physics and chemistry. Others have scarely enlarged their teaching of geology at all. Some departments have even narrowed their interests. The commonest change has been to introduce new instrumentation into the traditional geological subjects. This has been an excellent start, and now new ideas are being introduced. Geophysics has traditionally been taught separately, as an offshoot of physics, with insufficient attention to the cornplexities of geology.

Attitudes toward the new discoveries are likely to be equally diverse. Integrated departments will be in a position to appreciate and test the new ideas. Others will want to have little to do with them and will say that the proposed theory is still unproved. This is quite true. One can never reconstruct the distant past with mathematical certainty. and in that sense continental drift has not been proved and, by its nature cannot ever be proved. Nevertheless, the coincidence of the three ratios is now so well established that it cannot be ignored. This coincidence must be underlain by some principle. Drift is the only explanation yet offered, and, for that reason, it may become widely accepted.

If, in this way, the precise pattern of continental drift in later geological time has been revealed, this discovery will have a great effect upon traditional subjects.

As R. T. Chamber" said in 1928, 'If we are to believe Wegener's hypothesis we must forget everything which has been learned in the last 70 years and start all over again.' This, fortunately, is an exaggeration, but the standard textbooks assume that drift has not occurred. Ii it has, in fact, been occurring at a relatively rapid rate, much of our teaching must have been nonsense. Isn't it time we changed? Is there not evidence of much weakness in methods, both geological and geophysical, which were too feeble to distinguish between drift and non-drift?

Studies of minerals, rocks and fossils as intrinsic objects are legitimate fields of science. If they are to be pursued, this should be done in the ,most efficient ways possible. The propertie of these objects suggest links with crystallography, chemistry and biology, respectively.

On the other hand, if the object of a department is to study the Earth, then it is clear that mineralogy. petrology and paleontology are tools and that they have not been very efficient ones. Clearly, less instruction should be given to geologists of the details of these and similar subjects in order that time can be found to study other techniques. principles of the Earth's behavior and a general view of world geology.

Consider, for example, palaeontology. It now seems evident that magnetic reversals provide a succession of dates, synchronous all over the world, which were frequent during the Tertiary, and less so before. This can test and aid paleontological correlations and extend them to lava flows and other nonfossiliferous rocks. Many palaeontologists have tackled the problem of continental drift and they have come to such diverse and opposite views that one is forced to conclude that the study of fossils alone has not been a powerful enough method to resolve the matter. On the other hand, these new techniques promise to make some precise reconstructions possible. As the former relations of continents become known, the entire field of palaeontology will need reworking. The new proposals, far from eliminating the need for palaeontology, promise to aid this subject and place it on a much sounder basis, but this cannot be done without understanding the new theory. One should learn the powerful new theory first and palaeontology second. Palaeontology should increasingly be moved to graduate study.

In petrology, it is clearly important to be able to decide whether a volcano or other outlet for igneous rocks is remaining fixed over a source which it would tend to exhaust or whether it is moving about and thus continually drawing on fresh material. Conclusions about the origin of andesite, the common rock in island arcs, will surely be affected if it is decided that the ocean floors are not static, but are constantly being pushed -down in ocean trenches to pass under the arcs where 'he andesite is generated (Coats 1962). However, these important ideas have not been adequately considered. The chemistry of the Earth cannot be decided in the laboratory alone, but only when the laboratory is used as an aid to field work and new ideas.

Again, one cannot properly discuss structural geology without considering the implications of continental drift on the subject. Most of the existing textbooks do not. It has been suggested that many of the largest faults in the world are due to drift and hence are of a special type -transform faults- not previously recognized or described. There has been no time yet for any book on structural geology to even mention them.

If the continents are moving about they must react on one another. This can now be studied in a precise. way for Tertiary and Cretaceous time. Once the idea of relatively rapid drifting becomes accepted, its earlier history can he traced back using paleomagnetic and geological methods. This will modify Most of what has been written about historical geology. For example, the only modern book on world geology does not seriously entertain the idea of drift (Kummel 1961). Precambrian history can be sensibly interpreted only when many age determinations are combined with ideas about drift.

In geophysics, the patterns of magnetic anomalies over the oceans now make sense, gravity observations can be more easily interpreted and the processes that cause earthquakes can be better understood, Practically all courses and textbooks in stratigraphy, physics of the Earth, paleontology. petrology, and structural and historical geology have been rendered somewhat out of date and need revising. Under the circumstances, our ideas about economic geology and prospecting could not help but be vague and of little use.

It is thus apparent that the traditional methods in geology and in geophysics have not been as effective or as powerful as they could be in combination on a broader scale. The new discoveries have been made by utilizing all types of information on a worldwide basis-over oceans as well as over land, It is evident that the Earth is a single system, with all subjects and all regions reacting upon one another.

Heretofore, geophysics has been taught as one group of subjects and geology has been taught to other men as another. TO too great an extent, each subject has been treated as an isolated set of methods of data collecting and as a package of accummulated facts. Descriptive geology has been confined to a discussion of local areas and continents. To many, geophysics is only one specialized way of prospecting.

Clearly, all this is due to change. As fast as the details of the new story can be worked out and as fast as new books can be written, it is evident that earth science can be put on a similar basis as other sciences, with a discussion of the principles of the behavior of the Earth as the framework and the essential parts of the traditional subjects used to illustrate this. Regional geology must be discussed on a worldwide basis, not solely in terms of local details. Great adjustments in the curriculum are needed and room can only be found by removing, to the graduate school, the greater part of the work in those subjects which have proved to be less effective and less powerful.

The change that is needed is similar to the removal of much classical physics from undergraduate courses to make room for modern physics. No one has ever suggested that mechanics or acoustics were wrong. They are still used by specialists to track satellites and to design concert balls. On the other hand, everyone now agrees that it was wise to drop these undergraduate courses so that electronics, quantum mechanics, computer technology and other more powerful and more generally useful subjects could be taught. It is clear that the same pattern must be followed in geology and geophysics. 1 am not suggesting that the traditional subjects of geology are wrong. What 1 believe is that they can be better taught and more easily understood after the principles of Earth behavior are mastered. Most of the new techniques they employ are developments of physics, chemistry and mathematics, and geologists are correct in placing more stress on these courses. This change will take time and arouse opposition, but it is necessary if earth science is to rise to its opportunities. I can attest to the difficulty of conversion from my own experience.

This new approach is necessary if earth sciences are to attract students. Why should bright young scientists elect to study subjects mulled over for a century, shown to be ineffective in coping with major problems of the Earth and often of only local interest when a more modern undergraduate curriculum can introduce him to the whole spectrum of Earth and planetary science? The full scope and the greatest appeal of the subject lie in pointing out that now is the time when other planets are being explored, when the sea floor is yielding exciting discoveries, when the interior of the planets is becoming understood and when jet airplanes, helicopters and flying sensors are carrying out prospecting work all over the world.

This is the introduction that will appeal to, and be a sound basis for, our undergraduates. There may be a question of who, with that training, would do the necessary routine jobs, such as mapping. 1 believe the answer is that earth science is not now as effective as it might be and is not attracting many students. If modernized, it might be more useful and would attract more students who could do a better job.

effect on industry

The mining and petroleum industries want men in the earth sciences who can find useful deposits and they want more of them. Industry has always provided the greatest rewards and the highest praise to the successful prospectors and the great oil-finders. To find an orebody or a petroleum reservoir requires a theory in order to know where to drill. Today, that theory is more likely to be based upon an assessment of combined geological, geophysical and geochemical data than on a wildcatter's bunch. The broad training proposed is what is needed in industry. Geology has, in the past, lacked theories and this has been a serious defect as far as industry is concerned, A precise theory has now been proposed. It may have immediate benefits, but the most promising aspect is that discoveries in other sciences have rarely come singly. Witness the great succession of revolution in physics between 1895 and 1920. There is the same promise in the earth sciences.

Some immediate effects can, however, be stated. For the petroleum industry, these effects will be least in young strata in the heart of continents. In older rocks. and especially those which lie near coasts; the acceptance of drift will serve to explain why very great Volumes of sediments seem in some places to have been derived from areas that are now ocean. Borderlands, as envisioned by Barrell and Schuchert, are not Only possible but likely. Continental blocks have apparentetly been drifting together and breaking apart repeatedly (Wilson 1966). This may explain thrusting and rifling.

The movements of continents can explain changes from marine to continental to evaporite conditions. Thus, Belmonte, Hirtz & Wenger (1965) have suggested that the salt domes and oil deposits of Gabon and of the opposite coast of Brazil were formed as those continents started to break apart and the sea first entered the rift opening in mid-Cretaceous time.

The largest effects are to be expected in offshore oil basins. Continental drift can explain why the Gulf of Mexico may have been a small evaporite basin during Jurassic time and hence why there seern to be Wt domes on its floor under 12,000 ft of water. Drift would make possible very large strike-slip faults along the south side of the Grand Banks and off the equatorial coast of West Africa. If these am transform faults, they need never have penetrated the continents. a situation that would be impossible without drift and not previously envisioned in interpretations.

Arguments based on geophysical studies over oceans can reinforce geo. logical arguments on land. Thus, Hamilton & Myers (1966) concluded from a long study of the geology of California that the San Andreas fault is moving at the rate of 6 cm per year. This happens to be precisely the value obtained by Vine & Wilson (1965) from a study of offshore magnetics.

In mining, the present theory could have a marked effect upon the interpretation of one type of large ultrabasic body with associated copper and nickel deposits. Gass & Masson-Smith (1963) and Maxwell suggest that these bodies in Cyprus, and presumably also in Cuba. Italy, Turkey, Greece, New Caledonia and New Guinea, have been thrust up from the sea floor over the land. This interpretation has not been previously placed on these areas and the change could make a large difference in Prospecting.

Again, it is well known that no deposits have been found along some large faults, like the Great Glen in Scotland, whereas others, like the Kirkland Lake break or certain faults in British Columbia and California, are well mineralized. Perhaps the new theory can explain the difference and draw attention to new and favorable localities. It may do the same for batholiths and their associated ores. It is becoming evident that the building of the Andes and the Cordillera, with their important ore deposits. is likely to have been a consequence of the movements which opened the Atlantic Ocean. The whole subject of economic geology is ripe for a deeper understanding.

demand and need

As I have said, the proposals 1 have made for changing university curriculums are certain to meet with opposition. What amazes me is that the opposition is not greater. This winter, the leaders of several large and formerly very conservative university departments have radically altered their views. At the Geological Society of America's regional meeting in Boston in March 1967, 1 discovered that new editions of some of the leading American textbooks will soon appear, incorporating the new ideas. Earth scientists knew that their subject was ripe for a change, and their conversion to the new ideas has often been rapid.

The remaining opposition is chiefly based on the view that there is still a good demand for conventional geologists, so why change? Of course, all science graduates get jobs today, because there are not enough of them. Many conventional geologists are now going into school teaching, which is desirable, but this does nothing to meet the needs of industry, which wants men trained in all methods of prospecting.

The Geological Association of Canada suggests 'that the tendency for many graduates to continue research in areas not applicable to mineral exploration . . . considerably limits the 'number entering the industrial field.' (Canada 1966). The Association also mentions the demand for teachers. The American Association of Petroleum Geologists made a review which states that the supply of graduates in geology is about equal to demand, while the supply of geophysicists is only one-tenth of the demand (Royds et a]. 1965).

'Me concept that every professor should be free to do whatever research he wishes and should be supported is a popular one and has its merits. The chief claim is that only in this way can new ideas freely start. 1 believe that, for modest grants, the system is sound.

Anyone who has sat on several grant-awarding bodies will see other less desirable influences. The system provides no incentive to productivity. On the contrary, because many economically minded geologists work with industry in such a way that they do little research, the grants tend to he concentrated in those fields which are of the least economic interest. Another feature of the system seems to work against originality. the very aspect which the system was designed to encourage. Grant-giving bodies seem usually to he faced with a multitude of requests in a few fields and with none at all in others which seem to offer equal or greater opportunities. This has often come about because it happened that, a generation or more ago, one or two good teachers in one subject attracted many good students and thus started a tradition. These men all want to continue research in that field and the system offers no encouragement for anyone to change and enter new fields.

Three methods can be used to offset this. First, government bodies can and do encourage lagging fields by extra grants. Second, a major scientific discovery attracts good new workers. This happened when modern physics replaced classical physics as the center of interest and resulted in the preponderant emphasis on nuclear physics today. Third, it would help if industry stated their needs. If the mining and petroleum industries want more miners, geologists and geophysicists, they should say so more clearly. To many city students, the industry is only heard as a small and isolated voice from the distant and unattractive backwoods. Most Canadians have never seen a mine or an oil derrick. This is a very different situation from that in South Africa, where the largest city is also a mining camp. Alberta is an exception in that there are oil wells near cities.

The industry could get better results without even spending any more money. Existing scholarships and advertising could be more specifically directed to meeting needs. of course, some companies already do a great deal through summer employment and scholarships. An outstanding example of this has been provided by Geophysical Service Inc., which, for 16 years in the United States and for 2 years in Canada, has conducted orientation sessions for their summer students. Dr Cecil Green started these schemes with the altruistic view of aiding education, but the effect has been to encourage many top students to enter the earth sciences (Shrock 1966).

In spite of many excellent individual efforts, there is no industry-wide program in Canada. The pulp and paper industry, on the other hand, supports a research institute, and in South Africa the Chamber of Mines supports an Economic Geology Research Unit in the University of Witwatersrand. Granted that conditions are not the same, but these efforts do deserve consideration.

Agriculture, which is to be seen everywhere, is no more important to the Canadian economy than mining, but it gets a great deal more help from universities, both through specialized agricultural colleges and through research in biology. The mining industry needs men and it needs basic research into the Earth to help prospecting. Both of these are best provided by universities, but, at a time when good science students have so many attractive alternatives, no industry is likely to interest the better students without saying it needs them and without presenting a modern attractive and clearly visible appearance. I believe it is fair to say that, in the opinion of most other scientists, neither geologists nor prospectors have appeared to understand properly the, meaning of basic research. This is not because of any fault on the part of geologists. It is because the Earth is so complex that they have been limited to collecting data. The Earth is so much more complex than any of these matters studied in physics and chemistry that the science of geology has been correspondingly less developed. Suddenly, earth scientists appear to have been presented with two great opportunities.

The discovery of principles is always more exciting and more useful in science than the collection of data alone. It appears that a great new principle in Earth behavior may have just been discovered. This should be quickly and vigorously explored and exploited. It seems that we know now what is going on in the Earth. This could he as important to geology as Harvey's discovery of the circulation of the blood was to physiology or as evolution was to biology. This is the most exciting event in geology for a century and every effort in, research should be bent toward it.

In the second place, it appears to follow that the Earth and its economic deposits are part of a system-an Earth system-all parts of which react on other parts. New methods for the first time give us the opportunity to explore the whole system-its interior and its ocean floors as well as its land surface. We are on the verge of exploring other nearby planetary systems. Orebodies and oil structures are parts of that system, not just accidents.

What an exciting challenge this is! What a chance for great discoveries! What an appeal to young men! We must realize that a great change has occurred, If we are to take advantage of it we must radically broaden our views and change our habits.

Ir al debate entre Beloussov y Tuzo Wilsom         

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