A Short History of Nearly Everything: Special Illustrated Edition

by Bill Bryson

  Running for more than 800 miles, the San Andreas Fault in California is both the most famous and in places most visible of tectonic scars, the result of earlier lateral movements. Seen here as it crosses the Carrizo Plain near San Luis Obispo, it marks the point where two tectonic plates meet. For an outline of the Earth’s principal plates, see here. (credit 12.1)

  THE EARTH MOVES

  In one of his last professional acts before his death in 1955, Albert Einstein wrote a short but glowing foreword to a book by a geologist named Charles Hapgood entitled Earth’s Shifting Crust: A Key to Some Basic Problems of Earth Science. Hapgood’s book was a steady demolition of the idea that continents were in motion. In a tone that all but invited the reader to join him in a tolerant chuckle, Hapgood observed that a few gullible souls had noticed “an apparent correspondence in shape between certain continents.” It would appear, he went on, “that South America might be fitted together with Africa, and so on…It is even claimed that rock formations on opposite sides of the Atlantic match.”

  Mr. Hapgood briskly dismissed any such notions, noting that the geologists K. E. Caster and J. C. Mendes had done extensive fieldwork on both sides of the Atlantic and had established beyond question that no such similarities existed. Goodness knows what outcrops Messrs. Caster and Mendes had looked at, because in fact many of the rock formations on both sides of the Atlantic are the same—not just very similar but the same.

  This was not an idea that flew with Mr. Hapgood, or many other geologists of his day. The theory Hapgood alluded to was one first propounded in 1908 by an amateur American geologist named Frank Bursley Taylor. Taylor came from a wealthy family and had both the means and the freedom from academic constraints to pursue unconventional lines of enquiry. He was one of those struck by the similarity in shape between the facing coastlines of Africa and South America, and from this observation he developed the idea that the continents had once slid around. He suggested—presciently, as it turned out—that the crunching together of continents could have thrust up the world’s mountain chains. He failed, however, to produce much in the way of evidence, and the theory was considered too crackpot to merit serious attention.

  In Germany, however, Taylor’s idea was picked up, and effectively appropriated, by a theorist named Alfred Wegener, a meteorologist at the University of Marburg. Wegener investigated the many plant and fossil anomalies that did not fit comfortably into the standard model of Earth history and realized that very little of it made sense if conventionally interpreted. Animal fossils repeatedly turned up on opposite sides of oceans that were clearly too wide to swim. How, he wondered, did marsupials travel from South America to Australia? How did identical snails turn up in Scandinavia and New England? And how, come to that, did one account for coal seams and other semi-tropical remnants in frigid spots like Spitsbergen, over 600 kilometres north of Norway, if they had not somehow migrated there from warmer climes?

  Wegener developed the theory that the world’s continents had once existed as a single land mass he called Pangaea, where flora and fauna had been able to mingle, before splitting apart and floating off to their present positions. He set the idea out in a book called Die Entstehung der Kontinente und Ozeane, or The Origin of Continents and Oceans, which was published in German in 1912 and—despite the outbreak of the First World War in the meantime—in English three years later.

  Alfred Wegener, whose theory of continental drift was the first to attract widespread attention—but also widespread scorn. (credit 12.2)

  Because of the war, Wegener’s theory didn’t attract much notice at first, but by 1920, when he produced a revised and expanded edition, it quickly became a subject of discussion. Everyone agreed that continents moved—but up and down, not sideways. The process of vertical movement, known as isostasy, was a foundation of geological belief for generations, though no-one had any really good theories as to how or why it happened. One idea, which remained in textbooks well into my own schooldays, was the “baked apple” theory propounded by the Austrian Eduard Suess just before the turn of the century. This suggested that as the molten Earth had cooled, it had become wrinkled in the manner of a baked apple, creating ocean basins and mountain ranges. Never mind that James Hutton had shown long before that any such static arrangement would eventually result in a featureless spheroid as erosion levelled the bumps and filled in the divots. There was also the problem, demonstrated by Rutherford and Soddy early in the century, that earthly elements hold huge reserves of heat—much too much to allow for the sort of cooling and shrinking Suess suggested. And anyway, if Suess’s theory were correct, then mountains should be evenly distributed across the face of the Earth, which patently they were not, and of more or less the same ages; yet by the early 1900s it was already evident that some ranges, like the Urals and Appalachians, were hundreds of millions of years older than others, like the Alps and Rockies. Clearly the time was ripe for a new theory Unfortunately, Alfred Wegener was not the man geologists wished to provide it.

  Earth as it would have appeared 65 million years ago, at about the time the dinosaurs disappeared. Until quite recently, nearly all geologists would have dismissed such a picture of scattered continents as a physical impossibility. (credit 12.3)

  For a start, his radical notions questioned the foundations of their discipline, seldom an effective way to generate warmth in an audience. Such a challenge would have been painful enough coming from a geologist, but Wegener had no background in geology. He was a meteorologist, for goodness’ sake. A weatherman—a German weatherman. These were not remediable deficiencies.

  And so geologists took every pain they could to dismiss his evidence and belittle his suggestions. To get around the problems of fossil distributions, they posited ancient “land bridges” wherever they were needed. When an ancient horse named Hipparion was found to have lived in France and Florida at the same time, a land bridge was drawn across the Atlantic. When it was realized that ancient tapirs had existed simultaneously in South America and Southeast Asia a land bridge was drawn there, too. Soon maps of prehistoric seas were almost solid with hypothesized land bridges—from North America to Europe, from Brazil to Africa, from Southeast Asia to Australia, from Australia to Antarctica. These connective tendrils had not only conveniently appeared whenever it was necessary to move a living organism from one land mass to another, but then had obligingly vanished without leaving a trace of their former existence. None of this, of course, was supported by so much as a grain of evidence—nothing so wrong could be—yet it was geological orthodoxy for the next half-century.

  The Austrian geologist Eduard Suess, who suggested that the Earth’s wrinkled surface was due to the planet shrinking as it cooled. Although James Hutton had shown in the eighteenth century that such shrinkage was not possible, Suess’s theory would remain in textbooks into the middle of the twentieth century. (credit 12.4)

  Morning comes to the Great Smoky Mountains, part of the Appalachian range of eastern North America. By the early 1900s, geologists had established that the Appalachians were hundreds of millions of years older (and thus more rounded and eroded) than younger, more rugged ranges like the Alps and Rockies—a fact that didn’t sit well with prevailing geological theory. (credit 12.5)

  Even land bridges couldn’t explain some things. One species of trilobite that was well known in Europe was also found to have lived on Newfoundland—but only on one side. No-one could persuasively explain how it had managed to cross 3,000 kilometres of hostile ocean but then failed to find its way around the corner of an island 300 kilometres wide. Even more awkwardly anomalous was another species of trilobite found in Europe and the Pacific northwest of America but nowhere in between, which would have required not so much a land bridge as a flyover. Yet as late as 1964, when the Encyclopaedia Britannica discussed the rival theories it was Wegener’s that was held to be full of “numerous grave theoretical difficulties.” To be sure, Wegener made mistakes. He asserted that Greenland is drifting west by about
1.6 kilometres a year, a clear nonsense. (It’s more like a centimetre.) Above all, he could offer no convincing explanation for how the land masses moved about. To believe in his theory you had to accept that massive continents somehow pushed through solid crust, like a farm plough through soil, without leaving any furrow in their wake. Nothing then known could plausibly explain what motored these massive movements.

  It was Arthur Holmes, the English geologist who did so much to determine the age of the Earth, who came up with a suggestion. Holmes was the first scientist to understand that radioactive warming could produce convection currents within the Earth. In theory, these could be powerful enough to slide continents around on the surface. In his popular and influential textbook Principles of Physical Geology, first published in 1944, Holmes laid out a continental drift theory that was, in its fundamentals, the theory that prevails today. It was still a radical proposition for the time and widely criticized, particularly in the United States, where resistance to drift lasted longer than elsewhere. One reviewer there fretted, without any sense of irony, that Holmes presented his arguments so clearly and compellingly that students might actually come to believe them. Elsewhere, however, the new theory drew steady if cautious support. In 1950, a vote at the annual meeting of the British Association for the Advancement of Science showed that about half of those present now embraced the idea of continental drift. (Hapgood soon after cited this figure as proof of how tragically misled British geologists had become.) Curiously, Holmes himself sometimes wavered in his conviction. In 1953 he confessed: “I have never succeeded in freeing myself from a nagging prejudice against continental drift; in my geological bones, so to speak, I feel the hypothesis is a fantastic one.”

  Continental drift was not entirely without support in the United States. Reginald Daly of Harvard spoke for it, but he, you may recall, was the man who suggested that the Moon had been formed by a cosmic impact and his ideas tended to be considered interesting, even worthy, but a touch too exuberant for serious consideration. And so most American academics stuck to the belief that the continents had occupied their present positions for ever and that their surface features could be attributed to something other than lateral motions.

  Interestingly, oil company geologists had known for years that if you wanted to find oil you had to allow for precisely the sort of surface movements that were implied by plate tectonics. But oil geologists didn’t write academic papers; they just found oil.

  There was one other major problem with Earth theories that no one had resolved, or even come close to resolving. That was the question of where all the sediments went. Every year the Earth’s rivers carried massive volumes of eroded material—500 million tonnes of calcium, for instance—to the seas. If you multiplied the rate of deposition by the number of years it had been going on, you arrived at a disturbing figure: there should be about 20 kilometres of sediments on the ocean bottoms—or, put another way, the ocean bottoms should by now be well above the ocean tops. Scientists dealt with this paradox in the handiest possible way. They ignored it. But eventually there came a point when they could ignore it no longer.

  In the Second World War, a Princeton University mineralogist named Harry Hess was put in charge of an attack transport ship, the USS Cape Johnson. Aboard this vessel was a fancy new depth sounder called a fathometer, which was designed to facilitate inshore manoeuvres during beach landings, but Hess realized that it could equally well be used for scientific purposes and never switched it off, even when far out at sea, even in the heat of battle. What he found was entirely unexpected. If the ocean floors were ancient, as everyone assumed, they should be thickly blanketed with sediments, like the mud on the bottom of a river or lake. But Hess’s readings showed that the ocean floor offered anything but the gooey smoothness of ancient silts. It was scored everywhere with canyons, trenches and crevasses and dotted with volcanic seamounts that he called guyots after an earlier Princeton geologist named Arnold Guyot. All this was a puzzle, but Hess had a war to take part in, and put such thoughts to the back of his mind.

  After the war, Hess returned to Princeton and the preoccupations of teaching, but the mysteries of the sea floor continued to occupy a space in his thoughts. Meanwhile, throughout the 1950s oceanographers were undertaking more and more sophisticated surveys of the ocean floors. In so doing, they found an even bigger surprise: the mightiest and most extensive mountain range on Earth was—mostly—under water. It traced a continuous path along the world’s seabeds, rather like the pattern on a tennis ball. If you began at Iceland and travelled south, you could follow it down the centre of the Atlantic Ocean, around the bottom of Africa, and across the Indian and Southern oceans and into the Pacific just below Australia; there it angled across the Pacific as if making for Baja California before shooting up the west coast of the United States to Alaska. Occasionally its higher peaks poked above the water as an island or archipelago—the Azores and Canaries in the Atlantic, Hawaii in the Pacific, for instance—but mostly it was buried under thousands of fathoms of salty sea, unknown and unsuspected. When all its branches were added together, the network extended to 75,000 kilometres.

  A sea-floor graph made by Harry Hess of Princeton during the Second World War showing the presence of “guyots,” a formation that proved that the sea floor must be considerably younger than previously thought. (credit 12.6)

  A very little of this had been known for some time. People laying ocean-floor cables in the nineteenth century had realized that there was some kind of mountainous intrusion in the mid-Atlantic from the way the cables ran, but the continuous nature and overall scale of the chain was a stunning surprise. Moreover, it contained physical anomalies that couldn’t be explained. Down the middle of the mid-Atlantic ridge was a canyon—a rift—up to 20 kilometres wide for its entire 19,000-kilometre length. This seemed to suggest that the Earth was splitting apart at the seams, like a nut bursting out of its shell. It was an absurd and unnerving notion, but the evidence couldn’t be denied.

  Then in 1960 core samples showed that the ocean floor was quite young at the mid-Atlantic ridge but grew progressively older as you moved away from it to east or west. Harry Hess considered the matter and realized that this could mean only one thing: new ocean crust was being formed on either side of the central rift, then being pushed away from it as more new crust came along behind. The Atlantic floor was effectively two large conveyor belts, one carrying crust towards North America, the other carrying crust towards Europe. The process became known as sea-floor spreading.

  When the crust reached the end of its journey at the boundary with continents, it plunged back into the Earth in a process known as subduction. That explained where all the sediment went. It was being returned to the bowels of the Earth. It also explained why ocean floors everywhere were so comparatively youthful. None had ever been found to be older than about 175 million years, which was a puzzle because continental rocks were often billions of years old. Now Hess could see why. Ocean rocks lasted only as long as it took them to travel to shore. It was a beautiful theory that explained a great deal. Hess elaborated his arguments in an important paper, which was almost universally ignored. Sometimes the world just isn’t ready for a good idea.

  Workers lay telegraph cable at sea in this illustration from a French history of telegraphy of the late nineteenth century. Such expeditions first alerted engineers to the fact that ocean floors contained both canyons and mountains. (credit 12.7)

  Meanwhile, two researchers, working independently, were making some startling findings by drawing on a curious fact of Earth history that had been discovered several decades earlier. In 1906, a French physicist named Bernard Brunhes had found that the planet’s magnetic field reverses itself from time to time, and that the record of these reversals is permanently fixed in certain rocks at the time of their birth. Specifically, tiny grains of iron ore within the rocks point to wherever the magnetic poles happen to be at the time of their formation, then stay pointing in that direction
as the rocks cool and harden. In effect, they “remember” where the magnetic poles were at the time of their creation. For years this was little more than a curiosity, but in the 1950s Patrick Blackett of the University of London and S. K. Runcorn of the University of Newcastle studied the ancient magnetic patterns frozen in British rocks and were startled, to say the very least, to find them indicating that at some time in the distant past Britain had spun on its axis and travelled some distance to the north, as if it had somehow come loose from its moorings. Moreover, they also discovered that if you placed a map of Europe’s magnetic patterns alongside an American one from the same period, they fit together as neatly as two halves of a torn letter. It was uncanny. Their findings were ignored, too.

  It finally fell to two men from Cambridge University, a geophysicist named Drummond Matthews and a graduate student of his named Fred Vine, to draw all the strands together. In 1963, using magnetic studies of the Atlantic Ocean floor, they demonstrated conclusively that the sea floors were spreading in precisely the manner Hess had suggested and that the continents were in motion, too. An unlucky Canadian geologist named Lawrence Morley came up with the same conclusion at the same time, but couldn’t find anyone to publish his paper. In what has become a famous snub, the editor of the Journal of Geophysical Research told him: “Such speculations make interesting talk at cocktail parties, but it is not the sort of thing that ought to be published under serious scientific aegis.” One geologist later described it as “probably the most significant paper in the earth sciences ever to be denied publication.”