A Short History of Nearly Everything

by Bill Bryson

  Earth is alone among the rocky planets in having tectonics, and why this should be is a bit of a mystery. It is not simply a matter of size or density--Venus is nearly a twin of Earth in these respects and yet has no tectonic activity. It is thought--though it is really nothing more than a thought--that tectonics is an important part of the planet's organic well-being. As the physicist and writer James Trefil has put it, "It would be hard to believe that the continuous movement of tectonic plates has no effect on the development of life on earth." He suggests that the challenges induced by tectonics--changes in climate, for instance--were an important spur to the development of intelligence. Others believe the driftings of the continents may have produced at least some of the Earth's various extinction events. In November of 2002, Tony Dickson of Cambridge University in England produced a report, published in the journal Science , strongly suggesting that there may well be a relationship between the history of rocks and the history of life. What Dickson established was that the chemical composition of the world's oceans has altered abruptly and vigorously throughout the past half billion years and that these changes often correlate with important events in biological history--the huge outburst of tiny organisms that created the chalk cliffs of England's south coast, the sudden fashion for shells among marine organisms during the Cambrian period, and so on. No one can say what causes the oceans' chemistry to change so dramatically from time to time, but the opening and shutting of ocean ridges would be an obvious possible culprit.

  At all events, plate tectonics not only explained the surface dynamics of the Earth--how an ancient Hipparion got from France to Florida, for example--but also many of its internal actions. Earthquakes, the formation of island chains, the carbon cycle, the locations of mountains, the coming of ice ages, the origins of life itself--there was hardly a matter that wasn't directly influenced by this remarkable new theory. Geologists, as McPhee has noted, found themselves in the giddying position that "the whole earth suddenly made sense."

  But only up to a point. The distribution of continents in former times is much less neatly resolved than most people outside geophysics think. Although textbooks give confident-looking representations of ancient landmasses with names like Laurasia, Gondwana, Rodinia, and Pangaea, these are sometimes based on conclusions that don't altogether hold up. As George Gaylord Simpson observes in Fossils and the History of Life , species of plants and animals from the ancient world have a habit of appearing inconveniently where they shouldn't and failing to be where they ought.

  The outline of Gondwana, a once-mighty continent connecting Australia, Africa, Antarctica, and South America, was based in large part on the distribution of a genus of ancient tongue fern called Glossopteris, which was found in all the right places. However, much later Glossopteris was also discovered in parts of the world that had no known connection to Gondwana. This troubling discrepancy was--and continues to be--mostly ignored. Similarly a Triassic reptile called Lystrosaurus has been found from Antarctica all the way to Asia, supporting the idea of a former connection between those continents, but it has never turned up in South America or Australia, which are believed to have been part of the same continent at the same time.

  There are also many surface features that tectonics can't explain. Take Denver. It is, as everyone knows, a mile high, but that rise is comparatively recent. When dinosaurs roamed the Earth, Denver was part of an ocean bottom, many thousands of feet lower. Yet the rocks on which Denver sits are not fractured or deformed in the way they would be if Denver had been pushed up by colliding plates, and anyway Denver was too far from the plate edges to be susceptible to their actions. It would be as if you pushed against the edge of a rug hoping to raise a ruck at the opposite end. Mysteriously and over millions of years, it appears that Denver has been rising, like baking bread. So, too, has much of southern Africa; a portion of it a thousand miles across has risen nearly a mile in 100 million years without any known associated tectonic activity. Australia, meanwhile, has been tilting and sinking. Over the past 100 million years as it has drifted north toward Asia, its leading edge has sunk by some six hundred feet. It appears that Indonesia is very slowly drowning, and dragging Australia down with it. Nothing in the theories of tectonics can explain any of this.

  Alfred Wegener never lived to see his ideas vindicated. On an expedition to Greenland in 1930, he set out alone, on his fiftieth birthday, to check out a supply drop. He never returned. He was found a few days later, frozen to death on the ice. He was buried on the spot and lies there yet, but about a yard closer to North America than on the day he died.

  Einstein also failed to live long enough to see that he had backed the wrong horse. In fact, he died at Princeton, New Jersey, in 1955 before Charles Hapgood's rubbishing of continental drift theories was even published.

  The other principal player in the emergence of tectonics theory, Harry Hess, was also at Princeton at the time, and would spend the rest of his career there. One of his students was a bright young fellow named Walter Alvarez, who would eventually change the world of science in a quite different way.

  As for geology itself, its cataclysms had only just begun, and it was young Alvarez who helped to start the process.

  PART IV DANGEROUS PLANET

  13 BANG!

  PEOPLE KNEW FOR a long time that there was something odd about the earth beneath Manson, Iowa. In 1912, a man drilling a well for the town water supply reported bringing up a lot of strangely deformed rock--"crystalline clast breccia with a melt matrix" and "overturned ejecta flap," as it was later described in an official report. The water was odd too. It was almost as soft as rainwater. Naturally occurring soft water had never been found in Iowa before.

  Though Manson's strange rocks and silken waters were matters of curiosity, forty-one years would pass before a team from the University of Iowa got around to making a trip to the community, then as now a town of about two thousand people in the northwest part of the state. In 1953, after sinking a series of experimental bores, university geologists agreed that the site was indeed anomalous and attributed the deformed rocks to some ancient, unspecified volcanic action. This was in keeping with the wisdom of the day, but it was also about as wrong as a geological conclusion can get.

  The trauma to Manson's geology had come not from within the Earth, but from at least 100 million miles beyond. Sometime in the very ancient past, when Manson stood on the edge of a shallow sea, a rock about a mile and a half across, weighing ten billion tons and traveling at perhaps two hundred times the speed of sound ripped through the atmosphere and punched into the Earth with a violence and suddenness that we can scarcely imagine. Where Manson now stands became in an instant a hole three miles deep and more than twenty miles across. The limestone that elsewhere gives Iowa its hard mineralized water was obliterated and replaced by the shocked basement rocks that so puzzled the water driller in 1912.

  The Manson impact was the biggest thing that has ever occurred on the mainland United States. Of any type. Ever. The crater it left behind was so colossal that if you stood on one edge you would only just be able to see the other side on a good day. It would make the Grand Canyon look quaint and trifling. Unfortunately for lovers of spectacle, 2.5 million years of passing ice sheets filled the Manson crater right to the top with rich glacial till, then graded it smooth, so that today the landscape at Manson, and for miles around, is as flat as a tabletop. Which is of course why no one has ever heard of the Manson crater.

  At the library in Manson they are delighted to show you a collection of newspaper articles and a box of core samples from a 1991-92 drilling program--indeed, they positively bustle to produce them--but you have to ask to see them. Nothing permanent is on display, and nowhere in the town is there any historical marker.

  To most people in Manson the biggest thing ever to happen was a tornado that rolled up Main Street in 1979, tearing apart the business district. One of the advantages of all that surrounding flatness is that you can see danger from a long way o
ff. Virtually the whole town turned out at one end of Main Street and watched for half an hour as the tornado came toward them, hoping it would veer off, then prudently scampered when it did not. Four of them, alas, didn't move quite fast enough and were killed. Every June now Manson has a weeklong event called Crater Days, which was dreamed up as a way of helping people forget that unhappy anniversary. It doesn't really have anything to do with the crater. Nobody's figured out a way to capitalize on an impact site that isn't visible.

  "Very occasionally we get people coming in and asking where they should go to see the crater and we have to tell them that there is nothing to see," says Anna Schlapkohl, the town's friendly librarian. "Then they go away kind of disappointed." However, most people, including most Iowans, have never heard of the Manson crater. Even for geologists it barely rates a footnote. But for one brief period in the 1980s, Manson was the most geologically exciting place on Earth.

  The story begins in the early 1950s when a bright young geologist named Eugene Shoemaker paid a visit to Meteor Crater in Arizona. Today Meteor Crater is the most famous impact site on Earth and a popular tourist attraction. In those days, however, it didn't receive many visitors and was still often referred to as Barringer Crater, after a wealthy mining engineer named Daniel M. Barringer who had staked a claim on it in 1903. Barringer believed that the crater had been formed by a ten-million-ton meteor, heavily freighted with iron and nickel, and it was his confident expectation that he would make a fortune digging it out. Unaware that the meteor and everything in it would have been vaporized on impact, he wasted a fortune, and the next twenty-six years, cutting tunnels that yielded nothing.

  By the standards of today, crater research in the early 1900s was a trifle unsophisticated, to say the least. The leading early investigator, G. K. Gilbert of Columbia University, modeled the effects of impacts by flinging marbles into pans of oatmeal. (For reasons I cannot supply, Gilbert conducted these experiments not in a laboratory at Columbia but in a hotel room.) Somehow from this Gilbert concluded that the Moon's craters were indeed formed by impacts--in itself quite a radical notion for the time--but that the Earth's were not. Most scientists refused to go even that far. To them, the Moon's craters were evidence of ancient volcanoes and nothing more. The few craters that remained evident on Earth (most had been eroded away) were generally attributed to other causes or treated as fluky rarities.

  By the time Shoemaker came along, a common view was that Meteor Crater had been formed by an underground steam explosion. Shoemaker knew nothing about underground steam explosions--he couldn't: they don't exist--but he did know all about blast zones. One of his first jobs out of college was to study explosion rings at the Yucca Flats nuclear test site in Nevada. He concluded, as Barringer had before him, that there was nothing at Meteor Crater to suggest volcanic activity, but that there were huge distributions of other stuff--anomalous fine silicas and magnetites principally--that suggested an impact from space. Intrigued, he began to study the subject in his spare time.

  Working first with his colleague Eleanor Helin and later with his wife, Carolyn, and associate David Levy, Shoemaker began a systematic survey of the inner solar system. They spent one week each month at the Palomar Observatory in California looking for objects, asteroids primarily, whose trajectories carried them across Earth's orbit.

  "At the time we started, only slightly more than a dozen of these things had ever been discovered in the entire course of astronomical observation," Shoemaker recalled some years later in a television interview. "Astronomers in the twentieth century essentially abandoned the solar system," he added. "Their attention was turned to the stars, the galaxies."

  What Shoemaker and his colleagues found was that there was more risk out there--a great deal more--than anyone had ever imagined.

  Asteroids, as most people know, are rocky objects orbiting in loose formation in a belt between Mars and Jupiter. In illustrations they are always shown as existing in a jumble, but in fact the solar system is quite a roomy place and the average asteroid actually will be about a million miles from its nearest neighbor. Nobody knows even approximately how many asteroids there are tumbling through space, but the number is thought to be probably not less than a billion. They are presumed to be planets that never quite made it, owing to the unsettling gravitational pull of Jupiter, which kept--and keeps--them from coalescing.

  When asteroids were first detected in the 1800s--the very first was discovered on the first day of the century by a Sicilian named Giuseppi Piazzi--they were thought to be planets, and the first two were named Ceres and Pallas. It took some inspired deductions by the astronomer William Herschel to work out that they were nowhere near planet sized but much smaller. He called them asteroids--Latin for "starlike"--which was slightly unfortunate as they are not like stars at all. Sometimes now they are more accurately called planetoids.

  Finding asteroids became a popular activity in the 1800s, and by the end of the century about a thousand were known. The problem was that no one was systematically recording them. By the early 1900s, it had often become impossible to know whether an asteroid that popped into view was new or simply one that had been noted earlier and then lost track of. By this time, too, astrophysics had moved on so much that few astronomers wanted to devote their lives to anything as mundane as rocky planetoids. Only a few astronomers, notably Gerard Kuiper, the Dutch-born astronomer for whom the Kuiper belt of comets is named, took any interest in the solar system at all. Thanks to his work at the McDonald Observatory in Texas, followed later by work done by others at the Minor Planet Center in Cincinnati and the Spacewatch project in Arizona, a long list of lost asteroids was gradually whittled down until by the close of the twentieth century only one known asteroid was unaccounted for--an object called 719 Albert. Last seen in October 1911, it was finally tracked down in 2000 after being missing for eighty-nine years.

  So from the point of view of asteroid research the twentieth century was essentially just a long exercise in bookkeeping. It is really only in the last few years that astronomers have begun to count and keep an eye on the rest of the asteroid community. As of July 2001, twenty-six thousand asteroids had been named and identified--half in just the previous two years. With up to a billion to identify, the count obviously has barely begun.

  In a sense it hardly matters. Identifying an asteroid doesn't make it safe. Even if every asteroid in the solar system had a name and known orbit, no one could say what perturbations might send any of them hurtling toward us. We can't forecast rock disturbances on our own surface. Put them adrift in space and what they might do is beyond guessing. Any asteroid out there that has our name on it is very likely to have no other.

  Think of the Earth's orbit as a kind of freeway on which we are the only vehicle, but which is crossed regularly by pedestrians who don't know enough to look before stepping off the curb. At least 90 percent of these pedestrians are quite unknown to us. We don't know where they live, what sort of hours they keep, how often they come our way. All we know is that at some point, at uncertain intervals, they trundle across the road down which we are cruising at sixty-six thousand miles an hour. As Steven Ostro of the Jet Propulsion Laboratory has put it, "Suppose that there was a button you could push and you could light up all the Earth-crossing asteroids larger than about ten meters, there would be over 100 million of these objects in the sky." In short, you would see not a couple of thousand distant twinkling stars, but millions upon millions upon millions of nearer, randomly moving objects--"all of which are capable of colliding with the Earth and all of which are moving on slightly different courses through the sky at different rates. It would be deeply unnerving." Well, be unnerved because it is there. We just can't see it.

  Altogether it is thought--though it is really only a guess, based on extrapolating from cratering rates on the Moon--that some two thousand asteroids big enough to imperil civilized existence regularly cross our orbit. But even a small asteroid--the size of a house, say--could destroy a
city. The number of these relative tiddlers in Earth-crossing orbits is almost certainly in the hundreds of thousands and possibly in the millions, and they are nearly impossible to track.

  The first one wasn't spotted until 1991, and that was after it had already gone by. Named 1991 BA, it was noticed as it sailed past us at a distance of 106,000 miles--in cosmic terms the equivalent of a bullet passing through one's sleeve without touching the arm. Two years later, another, somewhat larger asteroid missed us by just 90,000 miles--the closest pass yet recorded. It, too, was not seen until it had passed and would have arrived without warning. According to Timothy Ferris, writing in the New Yorker , such near misses probably happen two or three times a week and go unnoticed.

  An object a hundred yards across couldn't be picked up by any Earth-based telescope until it was within just a few days of us, and that is only if a telescope happened to be trained on it, which is unlikely because even now the number of people searching for such objects is modest. The arresting analogy that is always made is that the number of people in the world who are actively searching for asteroids is fewer than the staff of a typical McDonald's restaurant. (It is actually somewhat higher now. But not much.)