A Short History of Nearly Everything: Special Illustrated Edition

by Bill Bryson

  “At least, we thought it was a collaboration,” said Anderson, producing a small pained smile.

  “It was a real learning curve for us,” Witzke went on. “There was actually quite a lot of bad science going on throughout the period—people rushing in with results that didn’t always stand up to scrutiny.” One of those moments came at the annual meeting of the American Geophysical Union in 1985, when Glenn Izett and C. L. Pillmore of the US Geological Survey announced that the Manson crater was of the right age to have been involved with the dinosaurs’ extinction. The declaration attracted a good deal of press attention but was unfortunately premature. A more careful examination of the data revealed that Manson was not only too small, but also nine million years too early.

  The first Anderson or Witzke learned of this setback to their careers was when they arrived at a conference in South Dakota, and found people coming up to them with sympathetic looks and saying: “We hear you lost your crater.” It was news to them that Izett and the other USGS scientists had just announced refined figures revealing that Manson couldn’t after all have been the extinction crater.

  “It was pretty stunning,” recalls Anderson. “I mean, we had this thing that was really important and then suddenly we didn’t have it any more. But even worse was the realization that the people we thought we’d been collaborating with hadn’t bothered to share with us their new findings.”

  “Why not?”

  He shrugged. “Who knows? Anyway, it was a pretty good insight into how unattractive science can get when you’re playing at a certain level.”

  The search moved elsewhere. By chance, in 1990 one of the searchers, Alan Hildebrand of the University of Arizona, met a reporter from the Houston Chronicle who happened to know about a large, unexplained ring formation, 193 kilometres wide and 48 kilometres deep, under Mexico’s Yucatán Peninsula at Chicxulub, near the city of Progreso, about 950 kilometres due south of New Orleans. The formation had been found by Pemex, the Mexican oil company, in 1952—the year, coincidentally, that Gene Shoemaker first visited Meteor Crater in Arizona—but the company’s geologists had concluded that it was volcanic, in line with the thinking of the day. Hildebrand travelled to the site and decided fairly swiftly that they had their crater. By early 1991 it had been established to nearly everyone’s satisfaction that Chicxulub was the impact site.

  Still, many people didn’t quite grasp what an impact could do. As Stephen Jay Gould recalled in one of his essays: “I remember harboring some strong initial doubts about the efficacy of such an event…[W]hy should an object only six miles across wreak such havoc upon a planet with a diameter of eight thousand miles?”

  Artist’s impression of fragments of Comet Shoemaker-Levy 9 (named for Eugene Shoemaker and his colleague David Levy) beginning the first of a week-long chain of crashes into the gassy surface of Jupiter. The devastation was far greater than most scientists had expected. (credit 13.9)

  Conveniently, a natural test of the theory arose soon after when the Shoemakers and Levy discovered Comet Shoemaker-Levy 9, which they soon realized was headed for Jupiter. For the first time, humans would be able to witness a cosmic collision—and witness it very well, thanks to the new Hubble Space Telescope. Most astronomers, according to Curtis Peebles, expected little, particularly as the comet was not a coherent sphere but a string of twenty-one fragments. “My sense,” wrote one, “is that Jupiter will swallow these comets up without so much as a burp.” One week before the impact, Nature ran an article, “The Big Fizzle Is Coming,” predicting that the impact would constitute nothing more than a meteor shower.

  The impacts began on 16 July 1994, went on for a week and were bigger by far than anyone—with the possible exception of Gene Shoemaker—expected. One fragment, known as Nucleus G, struck with the force of about six million megatonnes—seventy-five times all the nuclear weaponry in existence. Nucleus G was only about the size of a small mountain, but it created wounds in the Jovian surface the size of Earth. It was the final blow for critics of the Alvarez theory.

  Luis Alvarez never knew of the discovery of the Chicxulub crater or of the Shoemaker-Levy comet, as he died in 1988. Shoemaker also died early On the third anniversary of the Jupiter collision, he and his wife were in the Australian outback, where they went every year to search for impact sites. On a dirt track in the Tanami Desert—normally one of the emptiest places on Earth—they came over a slight rise just as another vehicle was approaching. Shoemaker was killed instantly, his wife injured. Some of his ashes were sent to the Moon aboard the Lunar Prospector spacecraft. The rest were scattered around Meteor Crater.

  Anderson and Witzke no longer had the crater that killed the dinosaurs, “but we still had the largest and most perfectly preserved impact crater in the mainland United States,” Anderson said. (A little verbal dexterity is required to keep Manson’s superlative status. Other craters are larger—notably, Chesapeake Bay, which was recognized as being an impact site in 1994—but they are either offshore or deformed.) “Chicxulub is buried under two to three kilometres of limestone and mostly offshore, which makes it difficult to study,” Anderson went on, “while Manson is really quite accessible. It’s because it is buried that it is actually comparatively pristine.”

  I asked them how much warning we would receive if a similar hunk of rock were coming towards us today.

  A blazing meteor streaks across space en route to the Earth in an artist’s rendering. In fact, according to Ray Anderson of the University of Iowa, the rock wouldn’t burst into flame, and thus become visible, until it hit the Earth’s atmosphere—about one second before impact. The likelihood is that such a visitation would take us completely by surprise. (credit 13.10)

  “Oh, probably none,” said Anderson breezily. “It wouldn’t be visible to the naked eye until it warmed up and that wouldn’t happen until it hit the atmosphere, which would be about one second before it hit the Earth. You’re talking about something moving many tens of times faster than the fastest bullet. Unless it had been seen by someone with a telescope, and that’s by no means a certainty, it would take us completely by surprise.”

  How hard an impactor hits depends on a lot of variables—angle of entry, velocity and trajectory, whether the collision is head-on or from the side, and the mass and density of the impacting object, among much else—none of which we can know so many millions of years after the fact. But what scientists can do—and Anderson and Witzke have done—is measure the impact site and calculate the amount of energy released. From that they can work out plausible scenarios of what it must have been like—or, more chillingly, would be like if it happened now.

  An asteroid or comet travelling at cosmic velocities would enter the Earth’s atmosphere at such a speed that the air beneath it couldn’t get out of the way and would be compressed, as in a bicycle pump. As anyone who has used such a pump knows, compressed air grows swiftly hot, and the temperature below it would rise to some 60,000 Kelvin, or ten times the surface temperature of the Sun. In this instant of its arrival in our atmosphere, everything in the meteor’s path—people, houses, factories, cars—would crinkle and vanish like cellophane in a flame.

  One second after entering the atmosphere, the meteorite would slam into the Earth’s surface where the people of Manson had a moment before been going about their business. The meteorite itself would vaporize instantly, but the blast would blow out 1,000 cubic kilometres of rock, earth and superheated gases. Every living thing within 250 kilometres that hadn’t been killed by the heat of entry would now be killed by the blast. Radiating outwards at almost the speed of light would be the initial shock wave, sweeping everything before it.

  For those outside the zone of immediate devastation, the first inkling of catastrophe would be a flash of blinding light—the brightest ever seen by human eyes—followed an instant to a minute or two later by an apocalyptic sight of unimaginable grandeur: a roiling wall of darkness reaching high into the heavens, filling one entire field of view and travelling
at thousands of kilometres an hour. Its approach would be eerily silent since it would be moving far beyond the speed of sound. Anyone in a tall building in Omaha or Des Moines, say, who chanced to look in the right direction would see a bewildering veil of turmoil followed by instantaneous oblivion.

  Within minutes, over an area stretching from Denver to Detroit and encompassing what had once been Chicago, St Louis, Kansas City, the Twin Cities—the whole of the Midwest, in short—nearly every standing thing would be flattened or on fire, and nearly every living thing would be dead. People up to 1,500 kilometres away would be knocked off their feet and sliced or clobbered by a blizzard of flying projectiles. Beyond 1,500 kilometres the devastation from the blast would gradually diminish.

  But that’s just the initial shock wave. No-one can do more than guess what the associated damage would be, other than that it would be brisk and global. The impact would almost certainly set off a chain of devastating earthquakes. Volcanoes across the globe would begin to rumble and spew. Tsunamis would rise up and head devastatingly for distant shores. Within an hour, a cloud of blackness would cover the Earth and burning rock and other debris would be pelting down everywhere, setting much of the planet ablaze. It has been estimated that at least a billion and a half people would be dead by the end of the first day. The massive disturbances to the ionosphere would knock out communications systems everywhere, so survivors would have no idea what was happening elsewhere or where to turn. It would hardly matter. As one commentator has put it, fleeing would mean “selecting a slow death over a quick one. The death toll would be very little affected by any plausible relocation effort, since Earth’s ability to support life would be universally diminished.”

  The amount of soot and floating ash from the impact and following fires would blot out the sun certainly for months, possibly for years, disrupting growing cycles. In 2001 researchers at the California Institute of Technology analysed helium isotopes from sediments left from the later KT impact and concluded that it affected the Earth’s climate for about ten thousand years. This was actually used as evidence to support the notion that the extinction of dinosaurs was swift and emphatic—and so it was, in geological terms. We can only guess how well, or whether, humanity would cope with such an event.

  And in all likelihood, remember, this would come without warning, out of a clear sky.

  But let’s suppose we did see the object coming. What would we do? Everyone assumes we would send up a nuclear warhead and blast it to smithereens. There are some problems with that idea, however. First, as John S. Lewis notes, our missiles are not designed for space work. They haven’t the oomph to escape Earth’s gravity, and even if they did there are no mechanisms to guide them across tens of millions of kilometres of space. Still less could we send up a shipload of space cowboys to do the job for us, as in the movie Armageddon; we no longer possess a rocket powerful enough to send humans even as far as the Moon. The last rocket that could, Saturn 5, was retired years ago and has never been replaced. Nor could we quickly build a new one because, amazingly, the plans for Saturn launchers were destroyed as part of a NASA spring-cleaning exercise.

  Even if we did manage somehow to get a warhead to the asteroid and blast it to pieces, the chances are that we would simply turn it into a string of rocks that would slam into us one after the other in the manner of Comet Shoemaker-Levy on Jupiter—but with the difference that now the rocks would be intensely radioactive. Tom Gehrels, an asteroid hunter at the University of Arizona, thinks that even a year’s warning would probably be insufficient to take appropriate action. The greater likelihood, however, is that we wouldn’t see any object—even a comet—until it was about six months away, which would be much too late. Shoemaker-Levy 9 had been orbiting Jupiter in a fairly conspicuous manner since 1929, but it was over half a century before anyone noticed.

  Because these things are so difficult to compute and must incorporate such a significant margin of error, even if we knew an object was heading our way we wouldn’t know until nearly the end—the last couple of weeks anyway—whether collision was certain. For most of the time of the object’s approach we would exist in a kind of cone of uncertainty. It would certainly be the most interesting few months in the history of the world. And imagine the party if it passed safely.

  “So how often does something like the Manson impact happen?” I asked Anderson and Witzke before leaving.

  “Oh, about once every million years on average,” said Witzke.

  “And remember,” added Anderson, “this was a relatively minor event. Do you know how many extinctions were associated with the Manson impact?”

  “No idea,” I replied.

  “None,” he said, with a strange air of satisfaction. “Not one.”

  Of course, Witzke and Anderson added hastily and more or less in unison, there would have been terrible devastation across much of the Earth, as just described, and complete annihilation for hundreds of miles around ground zero. But life is hardy, and when the smoke cleared there were enough lucky survivors from every species that none permanently perished.

  The good news, it appears, is that it takes an awful lot to extinguish a species. The bad news is that the good news can never be counted on. Worse still, it isn’t actually necessary to look to space for petrifying danger. As we are about to see, Earth can provide plenty of danger of its own.

  1 It is KT rather than CT because C had already been appropriated for Cambrian. Depending on which source you credit, the K comes from either the Greek kreta or the German Kreide. Both conveniently mean chalk, which is also what Cretaceous means.

  A jagged crack down a street indicates the sudden violence of the infamous earthquake that struck San Francisco on the morning of 18 April 1906. The quake and resulting fires left the city largely in ruins. (credit 14.1)

  THE FIRE BELOW

  In the summer of 1971, a young geologist named Mike Voorhies was scouting around on some grassy farmland in eastern Nebraska, not far from the little town of Orchard where he had grown up. Passing through a steep-sided gully, he spotted a curious glint in the brush above and clambered up to have a look. What he had seen was the perfectly preserved skull of a young rhinoceros, which had been washed out by recent heavy rains.

  A few yards beyond, it turned out, was one of the most extraordinary fossil beds ever discovered in North America: a dried-up waterhole that had served as a mass grave for scores of animals—rhinoceroses, zebra-like horses, sabre-toothed deer, camels, turtles. All had died from some mysterious cataclysm just under twelve million years ago in the time known to geology as the Miocene. In those days Nebraska stood on a vast, hot plain very like the Serengeti of Africa today. The animals had been found buried under volcanic ash up to 3 metres deep. The puzzle of it was that there were not, and never had been, any volcanoes in Nebraska.

  Today, the site of Voorhies’ discovery is called Ashfall Fossil Beds State Park. It has a stylish new visitors’ centre and museum, with thoughtful displays on the geology of Nebraska and the history of the fossil beds. The centre incorporates a lab with a glass wall through which visitors can watch palaeontologists cleaning bones. Working alone in the lab on the morning I passed through was a cheerfully grizzled-looking fellow in a blue workshirt whom I recognized as Mike Voorhies from a BBC Horizon documentary in which he had featured. They don’t get a huge number of visitors to Ashfall Fossil Beds State Park—it’s slightly in the middle of nowhere—and Voorhies seemed pleased to show me around. He took me to the spot atop a 6-metre-high ravine where he had made his find.

  “It was a dumb place to look for bones,” he said happily. “But I wasn’t looking for bones. I was thinking of making a geological map of eastern Nebraska at the time, and really just kind of poking around. If I hadn’t gone up this ravine or the rains hadn’t just washed out that skull, I’d have walked on by and this would never have been found.” He indicated a roofed enclosure nearby, which had become the main excavation site. There, some two hundred animals had b
een found lying together in a jumble.

  I asked him in what way it was a dumb place to hunt for bones. “Well, if you’re looking for bones, you really need exposed rock. That’s why most palaeontology is done in hot, dry places. It’s not that there are more bones there. It’s just that you have some chance of spotting them. In a setting like this“—he made a sweeping gesture across the vast and unvarying prairie—”you wouldn’t know where to begin. There could be really magnificent stuff out there, but there’s no surface clues to show you where to start looking.”

  At first they thought the animals were buried alive and Voorhies stated as much in a National Geographic article in 1981. “The article called the site a ‘Pompeii of prehistoric animals,’” he told me, “which was unfortunate because just afterwards we realized that the animals hadn’t died suddenly at all. They were all suffering from something called hypertrophic pulmonary osteodystrophy, which is what you would get if you were breathing a lot of abrasive ash—and they must have been breathing a lot of it because the ash was feet thick for hundreds of miles.” He picked up a chunk of greyish, claylike dirt and crumbled it into my hand. It was powdery but slightly gritty. “Nasty stuff to have to breathe,” he went on, “because it’s very fine but also quite sharp. So anyway they came here to this watering hole, presumably seeking relief, and died in some misery. The ash would have ruined everything. It would have buried all the grass and coated every leaf and turned the water into an undrinkable grey sludge. It couldn’t have been very agreeable at all.”

  The Horizon documentary had suggested that the existence of so much ash in Nebraska was a surprise. In fact, Nebraska’s huge ash deposits had been known about for a long time. For almost a century they had been mined to make household cleaning powders like Comet and Ajax. But, curiously, no-one had ever thought to wonder where all the ash came from.