A Short History of Nearly Everything: Special Illustrated Edition

by Bill Bryson

  “I’m a little embarrassed to tell you,” Voorhies said, smiling briefly, “that the first I thought about it was when an editor at the National Geographic asked me the source of all the ash and I had to confess that I didn’t know. Nobody knew.”

  Voorhies sent samples to colleagues all over the western United States asking if there was anything about it that they recognized. Several months later a geologist named Bill Bonnichsen from the Idaho Geological Survey got in touch and told him that the ash matched a volcanic deposit from a place called Bruneau-Jarbidge in southwest Idaho. The event that killed the plains animals of Nebraska was a volcanic explosion on a scale previously unimagined—but big enough to leave an ash layer 3 metres deep some 1,600 kilometres away in eastern Nebraska. It turned out that under the western United States there was a huge cauldron of magma, a colossal volcanic hot spot, which erupted cataclysmically every six hundred thousand years or so. The last such eruption was just over six hundred thousand years ago. The hot spot is still there. These days we call it Yellowstone National Park.

  Workers excavate the bones of grazing animals that died in a sudden—and for many years mysterious—cataclysm in Nebraska about 12 million years ago. The animals were buried under volcanic ash in a part of the country that had no volcanoes. (credit 14.1a)

  We know amazingly little about what happens beneath our feet. It is fairly remarkable to think that Ford has been building cars and Nobel committees awarding prizes for longer than we have known that the Earth has a core. And of course the idea that the continents move about on the surface like lily pads has been common wisdom for much less than a generation. “Strange as it may seem,” wrote Richard Feynman, “we understand the distribution of matter in the interior of the sun far better than we understand the interior of the earth.”

  The distance from the surface of Earth to the middle is 6,370 kilometres, which isn’t so very far. It has been calculated that if you sunk a well to the centre and dropped a brick down it, it would take only forty-five minutes for it to hit the bottom (though at that point it would be weightless since all the Earth’s gravity would be above and around it rather than beneath it). Our own attempts to penetrate towards the middle have been modest indeed. One or two South African gold mines reach to a depth of over 3 kilometres, but most mines on Earth go no more than about 400 metres beneath the surface. If the planet were an apple, we wouldn’t yet have broken through the skin. Indeed, we haven’t even come close.

  Until slightly under a century ago, what the best-informed scientific minds knew about Earth’s interior was not much more than what a coal miner knew—namely, that you could dig down through soil for a distance and then you’d hit rock, and that was about it. Then, in 1906, an Irish geologist named R. D. Oldham, while examining some seismograph readings from an earthquake in Guatemala, noticed that certain shock waves had penetrated to a point deep within the Earth and then bounced off at an angle, as if they had encountered some kind of barrier. From this he deduced that the Earth has a core. Three years later, a Croatian seismologist named Andrija Mohorovičić was studying graphs from an earthquake in Zagreb when he noticed a similar odd deflection, but at a shallower level. He had discovered the boundary between the crust and the layer immediately below, the mantle; this zone has been known ever since as the Mohorovičić discontinuity, or Moho for short.

  We were beginning to get a vague idea of the Earth’s layered interior—though it really was only vague. Not until 1936 did a Danish scientist named Inge Lehmann, studying seismographs of earthquakes in New Zealand, discover that there were two cores—an inner one, which we now believe to be solid, and an outer one (the one that Oldham had detected), which is thought to be liquid and the seat of magnetism.

  R. D. Oldham, the Irish geologist whose studies of earthquake waves in the early twentieth century led him to realize that the Earth has a core. (credit 14.2)

  At just about the time that Lehmann was refining our basic understanding of the Earth’s interior by studying the seismic waves of earthquakes, two geologists at Caltech in California were devising a way to make comparisons between one earthquake and the next. They were Charles Richter and Beno Gutenberg, though for reasons that have nothing to do with fairness the scale became known almost at once as Richter’s alone. (They were nothing to do with Richter, either. A modest fellow, he never referred to the scale by his own name, but always called it “the Magnitude Scale.”)

  The Richter scale has always been widely misunderstood by non-scientists, though it is perhaps a little less so now than in its early days when visitors to Richter’s office often asked to see his celebrated scale, thinking it was some kind of machine. The scale is, of course, more an idea than a thing, an arbitrary measure of the Earth’s tremblings based on surface measurements. It rises exponentially, so that a 7.3 quake is fifty times more powerful than a 6.3 earthquake and 2,500 times more powerful than a 5.3 earthquake.

  Theoretically, at least, there is no upper limit for an earthquake—nor, come to that, a lower limit. The scale is a simple measure of force, but says nothing about damage. A magnitude 7 quake happening deep in the mantle—say, 650 kilometres down—might cause no surface damage at all, while a significantly smaller one happening just 6 or 7 kilometres under the surface could wreak widespread devastation. Much, too, depends on the nature of the subsoil, the quake’s duration, the frequency and severity of aftershocks, and the physical setting of the affected area. All this means that the most fearsome quakes are not necessarily the most forceful, though force obviously counts for a lot.

  The largest earthquake since the scale’s invention was (depending on which source you credit) either one centred on Prince William Sound in Alaska in March 1964, which measured 9.2 on the Richter scale, or one in the Pacific Ocean off the coast of Chile in 1960, which was initially logged at 8.6 magnitude but later revised upwards by some authorities (including the US Geological Survey) to a truly grand-scale 9.5. As you will gather from this, measuring earthquakes is not always an exact science, particularly when it involves interpreting readings from remote locations. At all events, both quakes were whopping. The 1960 quake not only caused widespread damage across coastal South America, but also set off a giant tsunami that rolled nearly ten thousand kilometres across the Pacific and slapped away much of downtown Hilo, Hawaii, destroying five hundred buildings and killing sixty people. Similar wave surges claimed yet more victims as far away as Japan and the Philippines.

  Left: Charles Richter (far right) and a colleague from the California Institute of Technology investigate a stretch of buckled pavement following an earthquake. With Beno Gutenberg, Richter devised the famous scale that measures the magnitude of quakes. (credit 14.3a)

  Right: A page from one of Beno Gutenberg’s notebooks, with later annotations by Charles Richter. The name “Richter scale” was not used by Richter himself; he called it a “Magnitude Scale.” (credit 14.3b)

  For pure, focused devastation, however, probably the most intense earthquake in recorded history was one that struck—and essentially shook to pieces—Lisbon, Portugal, on All Saints Day (1 November), 1755. Just before ten in the morning, the city was hit by a sudden sideways lurch now estimated at magnitude 9.0 and shaken ferociously for seven full minutes. The convulsive force was so great that the water rushed out of the city’s harbour and returned in a wave over 15 metres high, adding to the destruction. When at last the motion ceased, survivors enjoyed just three minutes of calm before a second shock came, only slightly less severe than the first. A third and final shock followed two hours later. At the end of it all, sixty thousand people were dead and virtually every building for miles reduced to rubble. The San Francisco earthquake of 1906, for comparison, measured an estimated 7.8 on the Richter scale and lasted less than thirty seconds.

  Dazed citizens watch as central San Francisco is consumed by fire. The 1906 quake, estimated at 7.8 on the Richter scale, was not particularly violent and lasted for less than 60 seconds. Most of the damage came fr
om the subsequent fires. (credit 14.4)

  Earthquakes are fairly common. Every day on average somewhere in the world there are two of magnitude 2.0 or greater—that’s enough to give anyone nearby a pretty good jolt. Although they tend to cluster in certain places—notably around the rim of the Pacific—they can occur almost anywhere. In the United States, only Florida, eastern Texas and the upper Midwest seem—so far—to be almost entirely immune. New England has had two quakes of magnitude 6.0 or greater in the last two hundred years. In April 2002, the region experienced a 5.1 magnitude shaking in a quake near Lake Champlain on the New York-Vermont border, causing extensive local damage and (I can attest) knocking pictures from walls and children from beds as far away as New Hampshire.

  The most common types of earthquakes are those where two plates meet, as in California along the San Andreas Fault. As the plates push against each other, pressures build up until one or the other gives way. In general, the longer the interval between quakes, the greater the pent-up pressure and thus the greater the scope for a really big jolt. This is a particular worry for Tokyo, which Bill McGuire, a hazards specialist at University College London, describes as “the city waiting to die” (not a motto you will find on many tourism leaflets). Tokyo stands on the meeting point of three tectonic plates in a country already well known for its seismic instability. In 1995, as you will remember, the city of Kobe, nearly 500 kilometres to the west, was struck by a magnitude 7.2 quake, which killed 6,394 people. The damage was estimated at $99 billion. But that was as nothing—well, as comparatively little—compared with what may await Tokyo.

  Tokyo has already suffered one of the most devastating earthquakes in modern times. On 1 September 1923, just before midday, the city was hit by what is known as the Great Kanto quake—an event over ten times as powerful as Kobe’s earthquake. Two hundred thousand people were killed. Since that time, Tokyo has been eerily quiet, so the strain beneath the surface has been building for eighty years. Eventually it is bound to snap. In 1923, Tokyo had a population of about three million. Today it is approaching thirty million. Nobody cares to guess how many people might die, but the potential economic cost has been put as high as $7 trillion.

  Even more unnerving, because they are less well understood and capable of occurring anywhere at any time, are the rarer shakings of the type known as intraplate quakes. These happen away from plate boundaries, which makes them wholly unpredictable. And because they come from a much greater depth, they tend to propagate over much wider areas. The most notorious such quakes ever to hit the United States were a series of three in New Madrid, Missouri, in the winter of 1811–12. The adventure started just after midnight on 16 December when people were awakened first by the noise of panicking farm animals (the restiveness of animals before quakes is not an old wives’ tale, but is in fact well established, though not at all understood) and then by an almighty rupturing noise from deep within the Earth. Emerging from their houses, locals found the land rolling in waves up to a metre high and opening up in fissures several metres deep. A strong smell of sulphur filled the air. The shaking lasted for four minutes, with the usual devastating effects to property. Among the witnesses was the artist John James Audubon, who happened to be in the area. The quake radiated outwards with such force that it knocked down chimneys in Cincinnati over 600 kilometres away and, according to at least one account, “wrecked boats in East Coast harbors and…even collapsed scaffolding erected around the Capitol Building in Washington, D.C.” On 23 January and 4 February further quakes of similar magnitude followed. New Madrid has been silent ever since—but not surprisingly, since such episodes have never been known to happen in the same place twice. As far as we know, they are as random as lightning. The next one could be under Chicago or Paris or Kinshasa. No-one can even begin to guess. And what causes these massive intraplate rupturings? Something deep within the Earth. More than that, we don’t know.

  A fund-raising poster created after the devastating Great Kanto earthquake of 1923 in Tokyo, which killed 200,000 people in a city with just one-tenth the population of today. After eighty years without a significant tremor, Tokyo may well be overdue for another. (credit 14.5)

  By the 1960s scientists had grown sufficiently frustrated by how little they understood of the Earth’s interior that they decided to try to do something about it. Specifically, they got the idea to drill through the ocean floor (the continental crust was too thick) to the Moho discontinuity and to extract a piece of the Earth’s mantle for examination at leisure. The thinking was that if they could understand the nature of the rocks inside the Earth, they might begin to understand how they interacted, and thus possibly be able to predict earthquakes and other unwelcome events.

  The project became known, all but inevitably, as the Mohole, and it was pretty well disastrous. The hope was to lower a drill through over 4,000 metres of Pacific Ocean water off the coast of Mexico and drill some 5,000 metres through relatively thin crustal rock. Drilling from a ship in open waters is, in the words of one oceanographer, “like trying to drill a hole in the sidewalks of New York from atop the Empire State Building using a strand of spaghetti.” Every attempt ended in failure. The deepest they penetrated was only about 180 metres. The Mohole became known as the No Hole. In 1966, exasperated with ever-rising costs and no results, Congress killed the project.

  A 1969 children’s novel inspired by the brief notoriety of the Mohole project—an attempt to drill five kilometres through the Earth’s crust to find out exactly what lay beneath. Dogged by technical problems, the project was abandoned with the hole only 180 metres deep. (credit 14.6)

  Four years later, Soviet scientists decided to try their luck on dry land. They chose a spot on Russia’s Kola Peninsula, near the Finnish border, and set to work with the hope of drilling to a depth of 15 kilometres. The work proved harder than expected, but the Soviets were commendably persistent. When at last they gave up, nineteen years later, they had drilled to a depth of 12,262 metres. Bearing in mind that the crust of the Earth represents only about 0.3 per cent of the planet’s volume and that the Kola hole had not cut even one-third of the way through the crust, we can hardly claim to have conquered the interior.

  Even though the hole was modest, nearly everything about what it revealed surprised the researchers. Seismic wave studies had led the scientists to predict, and pretty confidently, that they would encounter sedimentary rock to a depth of 4,700 metres, followed by granite for the next 2,300 metres and basalt from there on down. In the event, the sedimentary layer was 50 per cent deeper than expected and the basaltic layer was never found at all. Moreover, the world down there was far warmer than anyone had expected, with a temperature at 10,000 metres of 180 degrees Celsius, nearly twice the forecast level. Most surprising of all was that the rock at depth was saturated with water—something that had not been thought possible.

  Because we can’t see into the Earth, we have to use other techniques, which mostly involve reading waves as they travel through the interior, to find out what is there. We know a little bit about the mantle from what are known as kimberlite pipes, where diamonds are formed. What happens is that deep in the Earth there is an explosion that fires, in effect, a cannonball of magma to the surface at supersonic speeds. It is a totally random event. A kimberlite pipe could explode in your back garden as you read this. Because they come up from such depths—up to 200 kilometres down—kimberlite pipes bring up all kinds of things not normally found on or near the surface: a rock called peridotite, crystals of olivine and—just occasionally, in about one pipe in a hundred—diamonds. Lots of carbon comes up with kimberlite ejecta, but most is vaporized or turns to graphite. Only occasionally does a hunk of it shoot up at just the right speed and cool down with the necessary swiftness to become a diamond. It was such a pipe that made South Africa the most productive diamond-mining country in the world, but there may be others even bigger that we don’t know about. Geologists know that somewhere in the vicinity of northeastern Indiana there
is evidence of a pipe or group of pipes that may be truly colossal. Diamonds up to 20 carats or more have been found at scattered sites throughout the region. But no-one has ever found the source. As John McPhee notes, it may be buried under glacially deposited soil, like the Manson crater in Iowa, or under the Great Lakes. So how much do we know about what’s inside the Earth? Very little. Scientists are generally agreed that the world beneath us is composed of four layers—a rocky outer crust, a mantle of hot, viscous rock, a liquid outer core and a solid inner core.1 We know that the surface is dominated by silicates, which are relatively light and not heavy enough to account for the planet’s overall density. Therefore there must be heavier stuff inside. We know that to generate our magnetic field somewhere in the interior there must be a concentrated belt of metallic elements in a liquid state. That much is universally accepted. Almost everything beyond that—how the layers interact, what causes them to behave in the way they do, what they will do at any time in the future—is a matter of at least some uncertainty, and generally quite a lot of uncertainty.

  Even the one part of it we can see, the crust, is a matter of some fairly strident debate. Nearly all geology texts tell you that continental crust is 5 to 10 kilometres thick under the oceans, about 40 kilometres thick under the continents and 65–95 kilometres thick under big mountain chains, but there are many puzzling variabilities within these generalizations. The crust beneath the Sierra Nevada Mountains, for instance, is only about 30–40 kilometres thick, and no one knows why. By all the laws of geophysics the Sierra Nevadas should be sinking, as if into quicksand. (Some people think they may be.)