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ALFRED WEGENER vs JUST ABOUT EVERYBODY ELSE: HOW THE CONTINENTS FORMED (1912 - 1960's)

This story has some very interesting features. It was a theory of how the continents, as we know them today, were formed, and it came at a time when Lord Kelvin's battles about the age of the Earth was just about at an end. It was proposed by a man, Alfred Lothar Wegener, who had essentially no training in geology; as you can imagine, a point not lost on his adversaries. Although as we look back it is essentially consistent with uniformitarianism, it seemed to have strong overtones of catastrophism, which was very much out of fashion at the time. The debate and differences between catastrophism and uniformitarianism were a common theme running through many of the scientific controversies. At the time of Wegener's premature death in 1930 his idea had been rejected by most geologists and for several decades it sank into obscurity. However, it was resurrected in the 1960's as part of the theory of what's called plate tectonics, and today, we have little problem with Wegener's ideas; in fact, they are the very foundation upon which all modern Earth science is based. When Wegener first suggested what we call today continental drift, the reaction was not only negative, it was so intense that many who were inclined to agree with him were genuinely frightened to come forward in case their own careers were put in jeopardy. For some 5 decades, its few

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proponents were dismissed contemptuously by scientists on both sides of the Atlantic and particularly strongly by those in the U.S. Although like the controversy over the age of the Earth, this particular feud may have lacked the true verbal venom and subtle wit of some the previous battles we have looked at it, is was, nevertheless, a long and hard battle for Wegener - and after his death, for his supporters - against the prevailing views of many of the world's leading authorities. In retrospect, we see that his theory showed remarkable insight, and it was undoubtedly his lack of formal training in geology and paleontology that enabled him to look at the Earth in a somewhat less restricted way than the highly disciplined "academic experts". He was able to take an objective view of all the available evidence and to see how it could all fit together.

Alfred Lothar Wegener was born on November 1, 1880 in Berlin, Germany. He was the youngest child of Dr. Richard Wegener, who was a strict evangelical preacher, and Anna Wegener (née Schwartz). He was brought up in comfortable circumstances. He attended the Köllnisches Gymnasium in Berlin and later studied at the universities of Heildelberg, Innsbruck and Berlin, earning a Ph.D degree in astronomy from the University of Berlin in 1905. In the meantime he had become interested in meteorology and paleoclimatology. He became second technical assistant to his brother Kurt at the Prussian Aeronautical Observatory in Tegel. Driven by

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dreams of exploring northern Greenland he would spend hours building up his endurance with long days of walking, skating, mountain climbing and skiing. He was a vigorous man, full of health, vitality and daring; in one escapade he and his brother, Kurt, carried out a balloon flight of 52 and1/2 hours; a record for that time. The flight began in Berlin and continued over Jutland and the Kattegat and then towards the Spessart area of Germany; considering the primitive equipment of the time was a particularly bold venture. However, the flight did provide a test of the the accuracy of the spirit-level clinometer as an instrument in flight navigation. He even proposed marriage to his wife - Elsa Koppen - during a balloon trip.

In 1906-1908 Alfred Wegener took part in a Danish national expedition to the northeast coast of Greenland to study polar air circulation. After his return he became a lecturer in astronomy and meteorology at the University of Marburg, and was considered a fine and popular teacher. His lectures formed the basis of his text book Thermodynamics of the Atmosphere, which had three editions. He made a second visit to Greenland in 1912-13 with J.P. Koch with the purpose of spending a winter at the eastern edge of the inland ice and then crossing Greenland at its widest part. He survived a threat of real danger during an ascent of a glacier that split. After camping over the winter, the crossing actually took place in 1913 and lasted two. The expedition

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was only just able to reach the west coast. He first presented his theory of what we now call continental drift in lectures in January 1912 and in several short articles, published in 1912. In 1915 he published it in full in 94 page book with the title The Origin of Continents and Oceans. The primary aim of the book was to re-establish the connections between geophysics, geogrpahy and geology; they had become identified as separate subjects nad had developed accordingly. The book was re-released in 1920, with an expanded index and more data. A third edition was published in 1922 and a fourth in 1929. Each edition was a complete revision with additional material included mainly as the result of criticisms.

Although in his formative years he was a robust and brave individual, he was by all accounts a peaceable man and that made his service as a reserve lieutenant in the Queen Elisabeth Grenadier Guards' Third Regiment during World War I particularly difficult for him. During the advance into Belgium he was shot through the arm. Some 14 days ater returning for duty a bullet lodged in his neck and he was declared unfit for active duty; he was then transferred to the army meteorological unit. If we remind ourselves the First World War took place between 1914-18 it seems remarkable that somehow during this period he produced a major, literally Earth shattering, book while on sick leave and while finishing the war in an army meteorological unit! In 1919

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Alfred, like his brother Kurt, became a departmental head at the German Marine Observatory in Hamburg and was also appointed as a lecturer at the newly founded University of Hamburg. In 1924 he was appointed to the Chair of Meteorology and Geophysics at the University of Graz, Austria, where he served until his death. Still very physically active as he approached 50 years old he was to make two more expeditions to Greenland. He had planned a new Greenland expedition with J.P Koch for 1928 but when Koch died it meant that the expedition became an all-German affair. Wegener obtained support from the German Research Association and in 1929 he made a brief visit to Greenland to find the most favorable route up the inland icecap from the west coast. The main expedition began in 1930 and they measured the thickness of inland ice at more than 1800 meters. But the expedition ended in disaster; Wegener died in November 1930 while attempting to cross from a camp on the central ice cap to the base camp on the west coast, And as I mentioned earlier, when he died in 1930 his theory drifted into limbo.

So, what was this theory and why the dissension? Why was it referred to as "preposterous, antiquated, a serious error, footloose" and even "dangerous"?

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Basically, what Wegener suggested in 1912 was that all of the Earth's continents formed, at one time in the distant past, a single, large land mass or supercontinent, called Pangaea and a single Ocean called Panthalassa, see, which had an average depth of about 2.64km (1.64 miles) and left only a small portion of the Earth's syrface exposed. The various continent that we see today started to break away from Pangaea about 200 to 250 million years ago and they have been moving over the surface of the Earth ever since. He used the word "continental displacement" to describe this movement, which later gave rise to the term "continental drift".

In fact, Wegener, was not the first to have the idea that the continents resulted from much larger land masses, Ever since the jigsaw fit of the continents became noticeable - and that occurred once reasonably accurate maps of the New World were available in the 16th century - there have been a variety of suggestions. Indeed, in his book, Wegener cites a number a number of other authors with generally similar views to his own that date back as far as 1857. Perhaps the earliest mention of drift and movement was by a Dutch cartographer named Abraham Ortelius around 1596. Francis Bacon also commented on the very similar shapes of South America and Africa in his Novem Organum of 1620. Apparently, around 1800, on noting the apparent fit of the bulge of eastern South America into the bight of western Africa, the German

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naturalist and explorer Alexander von Humboldt speculated that the lands bordering the Atlantic Ocean may once have been joined. Some 50 years later, in 1857 W.L.Green referred to

"segements of the earth's crust which float upon a liquid core".

In 1858, a French scientist, Antonio Snider-Pellegrini, argued that the existence of identical fossil plants in both North American and European coal deposits seem to suggest that the two continents were once connected. Then late in the 19th century the Austrian geologist Eduard Suess put forward the idea that several of the present continents had been formed from large ancient continents. However, he wasn't thinking of continental drift, but rather, as was the vogue in those days, that portions of a single enormous southern continent, which he called Gondawaland, sunk and produced the Atlantic and Indian Oceans. Also in 1910, the American Frank Taylor suggested that some of the world's mountain ranges were produced by the continents crashing into each other. In view of some of the similarities between Taylor's and Wegener's ideas some nationalistic Americans refer to the theory of continental drift as the Taylor-Wegener theory! However, it should be pointed out that Taylor was really only interested in how mountain chains were formed.

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At the turn of the 19th-20th centuries the scientific world was still ridding itself of Lord Kelvin's age-of-the-Earth calculations. Although the time was ripe for new theories on the prehistoric conditions on the planet, the prevailing idea of the vast majority of geologists at Wegener's time was that the Earth was once molten. Then the features we observe on the Earth, for example, the mountain ranges, gorges, canyons, etc., were formed as the Earth cooled and contracted from the molten state. They thought the peaks and valleys on the Earth's surface were formed just like the wrinkled skin of a shrinking, rotting apple; the low points were covered with water, the high points formed the continents. It was into this scene that Wegener was to cast his lot.

Apparently Wegener's first reference to any interest with the structure of the Earth's surface occurred in 1903 when he mentioned the jigsaw-puzzle fit of the continents to a fellow astronomy student. The development of his ideas is best reported in his own words in at the beginning of Chapter 1 of the fourth edition of his book:

"The first concept of continental drift first came to me as far back as 1910, when considering the map of the world, under the direct impression produced by the congruence of the coastlines on either side of the Atlantic. At first I did not pay attention to the idea because I regarded it as improbable.

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In the fall of 1911, I came quite accidentally upon a synoptic report in which I learned for the first time of palaeontological evidence for a former land bridge between Brazil and Africa. As a result I undertook a cursory examination of relevant research in the fields of geology and palaeontology, and this provided immediately such weighty corroboration that a conviction of the fundamental soundness of the idea took root in my mind. On the 6th of January 1912 I put forward the idea for the first time in an address to the Geological Association inFrankfurt am Main, entitled "The Geophysical Basis for the Evolution of the Large-Scale Features of the Earth's Crust (Continents and Oceans)"."

In truth, at the time he introduced the idea, continental drift was of peripheral interest to Wegener. Nevertheless, there is no getting away from the fact that his theory was well thought out for he had brought together evidence from a wide diversity of fields. Because his background was in astronomy, he owed no special allegiance to any one of the individual disciplines that made up the Earth Sciences. And that also provided him the insight to realize that his theory would impact vast areas of science. In the foreword of the 1928 edition of his book he wrote

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"The book is addressed equally to geodesists, geophysicists, geologists, paleontologists, zoogeopraphers, phytogeographers and paleoclimatologists. Its purpose is not only to provide research workers in these fields with an outline of the significance and usefulness of the drift theory as it applies to their own areas, but also mainly to orient them with regard to the applications and corroborations which the theory has found in areas other than their own."

Then, just as today, scientists in one discipline rarely read the papers or appreciated the discoveries of another discipline. So, in Wegener's day a zoo-geographer looking at the similarities between animal species in Africa and South America might never find out about the equally unusual correspondence of rock formations that would intrigue the geologists. Not only then did he consider the similarities between rock formations and living things both past and present, he was also free to look at the distribution of climates in the past, for example through glacial deposits and the evidence of tropical species in the northern and southern hemispheres. He read, for example, that fossils of various reptiles and plants dating back to the Permian and Triassic periods, that is back some 250-280 million years ago, were found throughout the southern continents; for example, a fern-like tree called Glossopteris existed in areas as widely separated as India, South Africa and Australia; that fossils of a freshwater reptile mesosaurus about 1m long were found in both South

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America and South Africa; that fossils of a land reptile cynognathus occurred in central South America and central Africa and fossils of another land reptile lystrosaurus were found in Antartica, India and central Africa. How could that be? ... it just didn't make any sense that the same fern would have developed independently and remain essentially identical in such widely separated regions. There were other examples of fossils as well. Taking a geological example; Wegener knew that there were large coal deposits in the islands of Spitzbergen, some 400 miles north of Norway. However, the appearance of coal suggests a tropical climate ... was Spitzbergen, now well above the Artic Circle, located at one time in tropical regions? Furthermore, he discovered that the plains of Africa showed evidence of having been the site of ancient glaciers ... could they have been, at some time in the distant past, much further north or further south? Wegener, the outsider, could take a broader view - or as we call it today, the global view! The fact that he read and reviewed the information from a range of disciplines was the important step. Unfortunately, it meant also that he had to spar with and confront a whole range of opponents each of whom viewed him as an interloper! Some of the reaction therefore was ... how dare you come into my back-yard, you outsider! Indeed, his own father-in-law, himself a respected meteorologist, was one of Wegener's earliest critics and tried to dissuade him from going outside his own area of expertise.

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Because it impacted a broad spectrum of disciplines the result was a theory that was not only dramatic but so all-embracing that few of his opponents felt they could attack it as a whole. And, there were a number areas where the details were could be attacked. Wegener did not claim to have all the answers nor could he, because rather like the case of Lord Kelvin, far less was known about the Earth than is known today. For example, the oceans cover over 70% of the Earth's surface and in Wegener's time there was no sonar, no deep-sea drilling, no underwater vessels, and so on, so he was forced to speculate about a number of details. (However, we mustn't take the similarity too far; remember, Lord Kelvin was wrong whereas Wegener was correct!) Wegener wanted people to believe in the overall picture rather than the fine details; he felt they could be filled in later.

Perhaps the most serious of the "fine details" was the mechanism. Wegener was convinced he was right - he once claimed that the chance of being wrong was less than one in a million - but he could not come up with a mechanism for the motion of the continents. The best he could do was to suggest two possibilities:

• the first he called polflucht, or pole-fleeing forces. These forces were due to the rotation of the Earth - a reaction to the centripetal force if you like - that caused the continents to move towards the Earth's equator,

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• the second, he attributed to some sort of tidal effect due to the gravitational forces of the Sun and Moon.

To be fair to Wegener, he suspected that these forces were not powerful enough but he had no other alternatives. However, this particular weakness provided ample ammunition for his critics. One of them, Harold Jeffreys, whose book The Earth, Its Origin, History and Physical Constitution (1924) was considered a classic, did some calculations and showed that the pole-fleeing and tidal forces were about one-millionth of the size needed to move the continents. Incidentally, in supporting the cooling theory Jeffreys produced a complicated theory involving cooling and differential contraction that, he claimed, provided the necessary forces to produce the landscape we see today.

In recognizing the shortcomings Wegener produced several editions of his book, each one heavily revised on the basis of new data and criticism. Indeed, in the 4th revised edition of his book, published in 1929, he said:

"In spite of all my efforts, many gaps, even important ones, will be found in this book."

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"The Newton of drift theory has not yet appeared. His absence need cause no anxiety; the theory is still young ..."

However, Jeffreys idea was one of the factors that effectively put Wegener's drift theory into the background around 1930. However, we are getting ahead of ourselves.

The first German edition of Wegener's Origin, only 94 pages long and without an index, actually caused little interest. The 1920 edition, also written in German, was much better organized, with more evidence and an index. It quickly caught the attention of scientists in Europe but to a large extent, their colleagues in the United States remained unaware of the storm that was brewing. That was until the third edition, published in 1924, was translated into several different languages, including French, English and Spanish. A fourth and final edition appeared in 1929.

Two important scientists - the Briton, Philip Lake and the American, Harry Fielding Reid - both wrote highly critical reviews that resulted in a chorus of attacks, including some that questioned Wegener's credibility as a scientist. For example, Lake complained

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"he is not seeking truth; he is advocating a cause, and is blind to every fact and argument that tells against it."

Lake added

"It is easy to fit the pieces of the puzzle together if you distort their shape, but when you have done so, your success is no proof that you have placed them in their original positions. It is not even proof that the pieces belong to the same puzzle, or that all of the pieces are present."

Other American scientists went after Wegener as well. Paleontologist E.W. Berry called the theory:

"a selective search through the literature for corroborative evidence, ignoring most of the facts that are opposed to the idea, and ending in a state of auto-intoxication in which the subjective idea comes to be considered as an objective fact."

The American geologist R. Thomas Chamberlain, whose father had been one of Lord Kelvin's strong adversaries,

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wondered whether geology could still be called a science if it is

"possible for such a theory as this to run wild."

Later, in 1928, at a symposium arranged by the American Association of Petroleum Geologists, Chamberlin was to complain

"If we are to believe in Wegener's hypothesis we must forget everything which has been learned in the past 70 years and start all over again."

Another respected American geologist Bailey Willis maintained that

"further discussion of it merely incumbers the literature and befogs the mind of fellow students. [It is] as antiquated as pre-Curie physics."

and adding that it was a

"fairy tale."

The strongest objections came from geophysicists who were challenging the mechanism he proposed. We have already mentioned Harold Jeffreys who showed that the strength and rigidity of the Earth's mantle over which the drift was taking place was far greater than the forces suggested by Wegener as the driving forces. Jeffreys called the drift idea

"a very dangerous one, and liable to lead to serious error."

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Wegener was attacked from many quarters and he found it difficult to control and respond to the onslaught. We can sense his frustration in this passage from a letter to his father-in-law; he wrote:

"Professor P.'s letter is typical! He will not allow himself to be taught. Those people who insist in treating only with the facts and want nothing to do with hypothesis, themselves are utilizing a false hypothesis without appreciating it! ... there is nothing in his letter about the struggle to get to the bottom of things, but only about the pleasure of exposing the limitations of other men."

Wegener felt that individual hits would not stifle the theory; but he was wrong. On the other hand, he believed the truth of the theory depended on bringing together the evidence from a variety of sources; in that, he was right. Although thoroughly outgunned he did have some supporters. One of the strongest was Alfred Holmes, a professor of geology at Edinburgh University, who pointed out that the lack of a driving force was hardly sufficient grounds to scuttle the entire concept. As early as 1929 Holmes postulated the idea of thermally induced convection currents in the Earth. It is rather like the swirling motion in a large pot of boiling water although not as fierce, of course! The heat at the bottom of the pot - which is like the center of the Earth in Holmes's theory - causes currents of water rise rise to the surface, spread out then fall back down at the cooler edges of the pot, Here, then, was a possible candidate for the driving force for

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the drift and Wegener included it in the 1929 edition of his book, the fourth and final edition. Although a promising advance, he was still unable to explain exactly how it would work. So, despite being essentially correct, he still lacked the final link in the chain. At about the same time he was to gain the support of one of the leading geologists of the time, the South African Alexander du Toit. du Toit had observed a striking similarity between the early geology of Africa and South America and after gathering some other evidence, he became not only an enthusiastic supporter of continental drift but a strong advocate as well. Wegener included some of du Toit's observations in his 1929 edition. But it was to no avail and following his death in 1930 attitudes seemed to harden and his theory had little general support. As a result of the highly negative voices raised against it, interest waned and the theory drifted into relative obscurity. In 1943, the American paleontologist George Gaylord Simpson expressed the prevailing view that existed through the 1930's, 40's and into the 50's when he argued

"... the distribution of mammals definitely supports the hypothesis that the continents were essentially stable throughout the whole time involved in mammalian history."

Only du Toit continued to amass further evidence. In fact, a sort of polarization occurred; through du Toit's efforts it remained quite respectable in the Southern Hemisphere to profess oneself a supporter of continental drift whereas in the Northern Hemisphere one would have been exposed to

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ridicule. In 1937 du Toit refined Wegener's hypothesis by suggesting that there were two primordial continents; Laurasia to the north and Gondwanaland to the south, that split further. However, it raised little interest.

So what happened next? There were two crucial developments in the 1950's and 60's that rekindled interest and eventually support for Wegener's hypothesis. The first involved studies of magnetism and the second following detailed studies of the Ocean floor.

The fact that some rocks are strongly magnetized has been known for centuries and well over a 100 years ago geologists recognized that many rocks preserve the imprint of the Earth's magnetic field in the direction it was when the rock was formed. Volcanic rocks are very good recorders because they are liquid initially and any magnetic particles experiencing the Earth's magnetic field become aligned - like a compass needle - and then "freeze" in that direction as the rock cools and solidifies. By studying old rocks, therefore, scientists can determine the direction of the Earth's magnetic pole at the time and place of solidification.

During the 1950's studies by British scientists led by Stanley Runcorn and Patrick Blackett produced some remarkable results. By studying the direction of the magnetic field in old rocks they showed that the north magnetic pole as seen from Europe appeared to have moved from an early position near Hawaii to its present location via Japan! There are two possible explanations for this observation, either:

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1. the continents were fixed and the magnetic pole had really truly moved around like that, or

2. the pole was fixed and it was Europe that had moved relative to the pole.

Similar measurements made on other continents also showed different "wandering" curves of the magnetic pole. However, the only way to achieve consistency with all these data was to assume that continents that are now separated were once joined. For example, the curves for Europe and North America can only be reconciled if it is assumed that America has drifted about 30 degrees to the west relative to Europe over the past 200 million years. Impressed by this result, Stanley Runcorn became the first of a new generation of geologists and geophysicists prepared to take continental drift seriously. Not everyone was convinced, yet, however, until further evidence was obtained from an entirely different source, namely, the Ocean floor.

Before looking at the new information let us look a bit more closely at Runcorn's measurements. Although the actual angular separation of the present coastlines of North America and Europe appears a little larger than 30 degrees we must remember two things; first, the actual coastline is continually modified by erosion and so on, and second, and more important, computer simulations indicates that the original edges of the continents actually corresponds to the present 1000 meter (3,300 ft) depth contours, which are closer together than the coastlines today. So, Runcorn's result

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was truly remarkable. OK then, what is the speed of separation? We can easily work that out; a 30 degree movement in 200 million years corresponds to a movement of 1.7 cm (or 2/3 inch) per year; i,e., about the speed that finger nails grow!

So what was this new information from the Ocean floor? As I mentioned earlier, in Wegener's time little was known about the Ocean floor. However, the presence of a major ridge midway between Europe and North America had been discovered during the laying of the transatlantic cable in the mid-1800's, but Wegener didn't think it had anything to do with his theory. During World War II defensive measures meant that rapid advances were made in the study of the relief, geology and geophysics of the Ocean basins, principally due to improvements in mapping equipment and mapping techniques. The results of these studies and others conducted during the ensuing "cold war" in the 50's and 60's had a major impact on the understanding of the drift processes that Wegener was unable to explain.

The first discovery was that the Mid-Atlantic Ridge was just one of many such underwater ridges. They form a sort of continuous seam around the Earth rather like the seam around a baseball. They can be huge, rising several kilometers in height from the Ocean floor and varying from a few hundred to 1,000's of kilometers wide. They are dotted here and there with submarine volcanoes, like black-smokers on the East Pacific Rise off Mexico, and volcanic islands, like

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the Galapagos, Ascension Island and, nearer home, Iceland. Although they look rather like submerged mountain chains they are quite different in shape and composition from anything on land. Other types of Ocean floor features were discovered; long, deep, but narrow trenches and fracture zones.

A second major discovery following the introduction by the Americans and the British of sophisticated seismometers around the world to monitor nuclear tests.. They found numerous underwater volcanic and earthquake-like events and if they were put together with the locations of known, previous earthquakes and volcanoes and curious pattern emerged.

Let's remember this but go back and concentrate on the ridges for a moment. A number of important discoveries were made:

1. material at the middle of the ridges proved to be hotter and much younger than material at some distance away from the ridge,

2. the Ocean crust has a different composition than continental crust,

3. no part of the Ocean floor was older than 200 million years.

By the late 1950's scientists also discovered that when they looked at the direction of the magnetic field lines there was a strange pattern of stripes running symmetrically along both sides of, and more or less parallel to the ridges, in which the

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direction alternated.. All these discoveries were puzzling, but an explanation was not long in coming.

The first comprehensive explanation was made by Harry Hess of Princeton University. Hess was a captain in the U.S. Navy during WWII. With the cooperation of his crew he took echo-sounding surveys of the sea-floor as he went from assignment to assignment during his service in the Pacific. He remained active in the naval reserve after joining Princeton, rising to the rank of rear Admiral. In a widely circulated manuscript that he had written in 1960 but not formally published for several years, he proposed the idea of sea-floor spreading.

Based on Holmes's model of convection, Hess suggested that hot material rose from the Earth's interior to the surface and then diverged producing the mid-ocean ridges. The material spread out in opposite directions to form the Ocean floor. That explained why the the material at the middle of the ridge was hotter and younger than material further away and why the composition of the sea-floor was different than the continents. The trenches were formed where the surface material descended back into the Earth's interior and that explained why the ocean floor was relatively speaking, young; it was being recycled! It was simple yet brilliant!

The magnetic field of the Earth is known to have reversed itself many times over time. The magnetic stripes were simply a manifestation of the changes in the direction of the Earth's magnetic field that occurred. When the rising hot material

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emerged and cooled it simply registered the direction of the field at that time.

Hess's idea is important for our story because it provides a possible mechanism for Wegener's continental drift. For, as Hess remarked

"The continents do not plough through oceanic crust impelled by unknown forces, rather they ride passively on mantle material as it comes to the surface at the crest of the ridge and then moves laterally away from it."

So, the continents are literally carried along by the process like objects on a conveyor belt.

Actually, continental drift became part of a recent theory, plate-tectonics. In this scenario it is not the individual continents that move; rather, the surface of the Earth is divided into maybe 30 hard, rigid plates of varying sizes; some are huge others are very small. The continents, and Oceans are located on these plates and it is these plates that actually move. It turns out the edges of the plates conform to the pattern of seismic activity that we mentioned before.. On average they are 60 miles thick, although they can vary from 5 miles thick to 120 miles. The current view is that the plates are rigid but they slide over very hot, flexible rock in the Earth's mantle.

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Where the edge of one plate meets another all kinds of things can happen.They can diverge, as we've already seen at the Mid-Atlantic Ridge. They can converge where one of the plates can descend below the other, or ride up on top of an opposing plate, or the two could mash together to form a mountain range. Examples include the Himalayas on the boundary between the Eurasian plate and the Indian/Australian plate and the Andes where the Pacific plate and the South American plate meet, or they could simply rub past each other, like at the San Andreas fault in California. Perhaps now you can see why volcanic and earthquake activity tends to take place at the plate boundaries, and why the boundaries then closely match the pattern of seismic activity I referred to just now.

Let's briefly look at the action at some of these boundaries. The Red Sea is the divergent boundary between the plates that carry Egypt and Saudi Arabia ... the Red Sea is actually growing wider! The formation of present day India is rather interesting. Originally, as we saw earlier, India was part of a land mass that later became Africa, Antartica and Australia. Literally, in the relatively recent past, i.e., that past 100 million years, India (on the Indian plate) seems to have travelled quite rapidly towards the Eurasian plate.. When the continents actually came into contact, about 10-20 million years ago, the Himalayas were formed. In fact, they are getting higher every year!

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Sometimes, as I said, the plates simply rub past each other, like the San Andreas fault in California. The sudden movement of one plate past the other causes earthquakes with the dislocations and offsets, we are familiar with.

So Wegener had been vindicated after all, some 50 years after the original proposal and 30 years of scientific limbo. His legacy lives on; much bigger, grander and more majestic than he could have imagined! But happily for today's geologists and geophysicists, many unanswered questions remain.

It seems remarkable to us today that Wegener's theory was given such a hostile reception and fell into obscurity in 1930. He displayed an enormous array of supporting evidence ranging from the similarities of sequences of strata and the continuity of folds on opposite sides of Oceans to paleobiological and paleoclimatic arguments that today would be judged worthy of serious consideration. A further question comes to mind ... like Darwin's theory of evolution, Wegener's theory is still incomplete and there are plenty of unresolved questions. And yet it is accepted without question. Then why isn't Darwin's theory accepted? Well maybe it's because there are far fewer religious implications in Wegener's theory and so it's easier to accept than Darwin's.

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Well, what will the continents look like 30 million years from now? The best guess is something like this ... the Atlantic Ocean is wider, the Pacific narrower, the West Indies now form the link between N and S America, part of California will have become detached and the islands in the Pacific and Indian Oceans will have change dramatically.

The kids at school in the future are going to have to remember a lot more island names than we had to!

So, our planet is not the quiet, unassuming place it appears from space. It is full of turmoil and constant change and I'm not talking politics!

As I look at the picture of the Earth rising above the Moon's horizon, I am reminded of the words of Claudius Ptolemy (ca. 90-170 AD):

"I know that I am mortal and the creature of a day; but when I search out the massed wheeling circles of the stars, my feet no longer touch the Earth, but, side by side with Zeus himself I take my fill of ambrosia, the food of the gods."