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PEOPLE KNEW FOR a long time that there was something odd about the earth behManson, Iowa. In 1912, a man drilling a well for the town water supply reported bringing up alot of strangely deformed rock—“crystalline clast breccia with a melt matrix” and “overtura flap,” as it was later described in an official report. The water was odd too. It wasalmost as soft as rainwater. Naturally soft water had never been found in Iowabefore.Though Manson’s strange rocks and silken waters were matters of curiosity, forty-oneyears would pass before a team from the Uy of Iowa got around to making a trip to theunity, then as now a town of about two thousand people in the northwest part of thestate. In 1953, after sinking a series of experimental bores, uy geologists agreed thatthe site was indeed anomalous and attributed the deformed rocks to some a, unspecifiedvolic a. This was in keeping with the wisdom of the day, but it was also about aswrong as a geological clusion get.
The trauma to Manson’s geology had e not from within the Earth, but from at least 100million miles beyond. Sometime in the very a past, when Manson stood on the edge of ashallow sea, a rock about a mile and a half across, weighing ten billion tons and traveling atperhaps two huimes the speed of sound ripped through the atmosphere and puo the Earth with a violend suddehat we scarcely imagine. Where Mansonnow stands became in an instant a hole three miles deep and more thay miles across.
The limestohat elsewhere gives Iowa its hard mineralized water was obliterated andreplaced 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 Uates. Of any type. Ever. The crater it left behind was so colossal that if you stood on oneedge you would only just be able to see the other side on a good day. It would make the Grandyon look quaint and trifling. Unfortunately for lovers of spectacle, 2.5 million years ofpassing ice sheets filled the Manson crater right to the top with rich glacial till, then graded itsmooth, 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 colle of neer articlesand a box of core samples from a 1991–92 drilling program—ihey positively bustle toproduce them—but you have to ask to see them. Nothing perma is on display, andnowhere iown is there any historical marker.
To most people in Manson the biggest thing ever to happen was a tornado that rolled upMain Street in 1979, tearing apart the business district. One of the advantages of all thatsurrounding flatness is that you see danger from a long way off. Virtually the whole townturned out at one end of Main Street and watched for half an hour as the tornado came towardthem, 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 weeklocalled Crater Days, which was dreamed up as a way of helping people fet that unhappyanniversary. It doesn’t really have anything to do with the crater. Nobody’s figured out a wayto capitalize on an impact site that isn’t visible.
“Very occasionally we get people ing in and asking where they should go to see thecrater and we have to tell them that there is nothing to see,” says Anna Schlapkohl, the town’sfriendly librarian. “Then they go away kind of disappointed.” However, most people,including most Iowans, have never heard of the Manson crater. Even feologists it barelyrates a footnote. But for one brief period in the 1980s, Manson was the most geologicallyexg pla Earth.
The story begins in the early 1950s when a bright young geologist named EugeneShoemaker paid a visit to Meteor Crater in Arizona. Today Meteor Crater is the most famousimpact site oh and a popular tourist attra. In those days, however, it didn’t receivemany visitors and was still often referred to as Barringer Crater, after a wealthy miningengineer named Daniel M. Barringer who had staked a claim on it in 1903. Barringer believedthat the crater had been formed by a ten-million-toeor, heavily freighted with iron andnickel, and it was his fident expectation that he would make a fortune digging it out.
Unaware that the meteor and everything in it would have been vaporized on impact, hewasted a fortune, and the wenty-six years, cutting tuhat yielded nothing.
By the standards of today, crater resear the early 1900s was a trifle unsophisticated, tosay the least. The leading early iigat. K. Gilbert of bia Uy, modeledthe effepacts by flinging marbles into pans of oatmeal. (For reasons I ot supply,Gilbert ducted these experiments not in a laboratory at bia but in a hotel room.)Somehow from this Gilbert cluded that the Moon’s craters were indeed formed byimpacts—in itself quite a radiotion for the time—but that the Earth’s were not. Moststists refused to go even that far. To them, the Moon’s craters were evidence of avoloes and nothing more. The few craters that remained evident oh (most had beeneroded away) were generally attributed to other causes or treated as fluky rarities.
By the time Shoemaker came along, a on view was that Meteor Crater had beenformed by an underground steam explosion. Shoemaker knew nothing about undergroundsteam explosions—he couldn’t: they do—but he did know all about blast zones. Oneof his first jobs out of college was to study explosis at the Yucca Flats est sitein Nevada. He cluded, as Barringer had before him, that there was nothing at MeteorCrater to suggest volic activity, but that there were huge distributions of other stuff—anomalous fine silicas and mages principally—that suggested an impact from space.
Intrigued, he began to study the subje his spare time.
W first with his colleague Eleanor Helin and later with his wife, Carolyn, andassociate David Levy, Shoemaker began a systematic survey of the inner solar system. Theyspent 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 beendiscovered iire course of astronomical observation,” Shoemaker recalled some yearslater in a television interview. “Astronomers iweh tury essentially abahe solar system,” he added. “Their attention was turo the stars, the galaxies.”
What Shoemaker and his colleagues found was that there was more risk out there—a greatdeal more—than anyone had ever imagined.
Asteroids, as most people know, are rocky objects orbiting in loose formation in a beltbetween Mars and Jupiter. In illustrations they are always shown as existing in a jumble, butin fact the solar system is quite a roomy plad the average asteroid actually will be abouta million miles from its neighbor. Nobody knows even approximately how manyasteroids there are tumbling through space, but the number is thought to be probably not lessthan a billion. They are presumed to be plahat never quite made it, owing to theuling gravitational pull of Jupiter, which kept—and keeps—them from coalesg.
When asteroids were first detected in the 1800s—the very first was discovered on the firstday of the tury by a Sicilian named Giuseppi Piazzi—they were thought to be plas, andthe first two were named Ceres and Pallas. It took some inspired dedus by theastronomer William Herschel to work out that they were nowhere near pla sized but muchsmaller. He called them asteroids—Latin for “starlike”—which was slightly unfortuhey are not like stars at all. Sometimes now they are more accurately called plaoids.
Finding asteroids became a popular activity in the 1800s, and by the end of the turyabout a thousand were known. The problem was that no one was systematically recthem. By the early 1900s, it had often bee impossible to know whether an asteroid thatpopped into view was new or simply ohat had been noted earlier and then lost track of. Bythis time, too, astrophysics had moved on so much that few astronomers wao devotetheir lives to anything as mundane as rocky plaoids. Only a few astronomers, notablyGerard Kuiper, the Dutch-born astronomer for whom the Kuiper belt of ets is ook any i in the solar system at all. Thanks to his work at the Mald Observatoryin Texas, followed later by work done by others at the Minor Pla ter in ati andthe Spacewatch proje Arizona, a long list of lost asteroids was gradually whittled downuntil by the close of the tweh tury only one known asteroid was unated for—a called 719 Albert. Last seen in October 1911, it was finally tracked down in 2000 afterbeing missing fhty-nine years.
So from the point of view of asteroid research the tweh tury was essentially just along exercise in bookkeeping. It is really only in the last few years that astronomers havebegun to t and keep an eye on the rest of the asteroid unity. As of July 2001,twenty-six thousand asteroids had been named and identified—half in just the previous twoyears. With up to a billion to identify, the t obviously has barely begun.
In a se hardly matters. Identifying an asteroid doesn’t make it safe. Even if everyasteroid in the solar system had a name and known orbit, no one could say erturbationsmight send any of them hurtling toward us. We ’t forecast rock disturbances on our ownsurface. Put them adrift in spad what they might do is beyond guessing. Any asteroid outthere 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 whichis crossed regularly by pedestrians who don’t know enough to look before stepping off thecurb. At least 90 pert of these pedestrians are quite unknown to us. We don’t know wherethey live, what sort of hours they keep, how often they e our way. All we know is that atsome point, at uain intervals, they trundle across the road down which we are cruising atsixty-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-crossingasteroids larger than about teers, there would be over 100 million of these objects in thesky.” In short, you would see not a couple of thousand distant twinkling stars, but millionsupon millions upon millions of nearer, randomly moving objects—“all of which are capableof colliding with the Earth and all of which are moving on slightly different courses throughthe sky at different rates. It would be deeply unnerving.” Well, be unnerved because it isthere. We just ’t see it.
Altogether it is thought—though it is really only a guess, based orapolating fromcratering rates on the Moon—that some two thousand asteroids big enough to imperilcivilized 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 ih-crossing orbits isalmost certainly in the hundreds of thousands and possibly in the millions, and they are nearlyimpossible to track.
The first one wasn’t spotted until 1991, and that was after it had already gone by. Named1991 BA, it was noticed as it sailed past us at a distance of 10<q>.９９ｌｉb.</q>6,000 miles—in ic termsthe equivalent of a bullet passing through one’s sleeve without toug the arm. Two yearslater, another, somewhat larger asteroid missed us by just 90,000 miles—the closest pass yetrecorded. It, too, was not seen until it had passed and would have arrived without warning.
Acc to Timothy Ferris, writing in the New Yorker, suear misses probably happentwo or three times a week and go unnoticed.
An object a hundred yards across couldn’t be picked up by ah-based telescope untilit was within just a few days of us, and that is only if a telescope happeo be trained on it,which is unlikely because even now the number of people searg for such objects ismodest. The arresting analogy that is always made is that the number of people in the worldwho are actively searg for asteroids is fewer thaaff of a typical Mald’srestaurant. (It is actually somewhat higher now. But not much.)While Gene Shoemaker was trying to get people galvanized about the potential dangers ofthe inner solar system, another development—wholly ued on the face of it—was quietlyunfolding in Italy with the work of a young geologist from the Lamont Doherty Laboratory atbia Uy. In the early 1970s, Walter Alvarez was doing fieldwork in a elydefile known as the Bottae Ge, he Umbrian hill town of Gubbio, when he grewcurious about a thin band of reddish clay that divided two a layers of limestone—onefrom the Cretaceous period, the other from the Tertiary. This is a point known to geology asthe KT boundary,1and it marks the time, sixty-five million years ago, when the dinosaurs androughly half the world’s other species of animals abruptly vanish from the fossil record.
Alvarez wondered what it was about a thin lamina of clay, barely a quarter of an inch thick,that could at for such a dramatient ih’s history.
At the time the ventional wisdom about the dinosaur extin was the same as it hadbeen in Charles Lyell’s day a tury earlier—hat the dinosaurs had died out overmillions of years. But the thinness of the clay layer clearly suggested that in Umbria, if1It is KT rather than CT because C had already been appropriated for Cambrian. Depending on which sourceyou credit, the K es either from the Greek Kreta erman Kreide. Both vely mean “chalk,” whichis also what Cretaeans.
nowhere else, something rather more abrupt had happened. Unfortunately in the 1970s s existed for determining how long such a deposit might have taken to accumulate.
In the normal course of things, Alvarez almost certainly would have had to leave theproblem at that, but luckily he had an impeccable e to someoside hisdiscipline who could help—his father, Luis. Luis Alvarez was an emi nuclear physicist;he had won the Nobel Prize for physics the previous decade. He had always been mildlysful of his son’s attat to rocks, but this problem intrigued him. It occurred to himthat the answer might lie in dust from space.
Every year the Earth accumulates some thirty thousaris of “icspherules”—space dust in plainer language—which would be quite a lot if you swept it intoone pile, but is infinitesimal when spread across the globe. Scattered through this thin dustingare exotic elements not normally much found oh. Among these is the element iridium,which is a thousand times more abundant in space than in the Earth’s crust (because, it isthought, most of the iridium oh sank to the core when the pla was young).
Alvarez khat a colleague of his at the Lawrence Berkeley Laboratory in California,Frank Asaro, had developed a teique for measuring very precisely the chemiposition of clays using a process called ron activation analysis. This involvedb samples with rons in a small nuclear reactor and carefully ting thegamma rays that were emitted; it was extremely finicky work. Previously Asaro had used theteique to analyze pieces of pottery, but Alvarez reasohat if they measured the amountof o<var></var>ne of the exotic elements in his son’s soil samples and pared that with its annual rateof deposition, they would know how long it had taken the samples to form. On an Octoberafternoon in 1977, Luis and Walter Alvarez dropped in on Asaro and asked him if he wouldrun the necessary tests for them.
It was really quite a presumptuous request. They were asking Asaro to devote months tomaking the most painstaking measurements of geological samples merely to firm whatseemed entirely self-evident to begin with—that the thin layer of clay had been formed asquickly as its thinness suggested. Certainly no one expected his survey to yield any dramaticbreakthroughs.
“Well, they were very charming, very persuasive,” Asaro recalled in an interview in 2002.
“And it seemed an iing challenge, so I agreed to try. Unfortunately, I had a lot of otherwork on, so it was eight months before I could get to it.” He sulted his notes from theperiod. “On June 21, 1978, at 1:45 p.m., we put a sample iector. It ran for 224minutes and we could see we were getting iis, so we stopped it and had alook.”
The results were so ued, in fact, that the three stists at first thought they had tobe wrong. The amount of iridium in the Alvarez sample was more than three huimesnormal levels—far beyond anything they might have predicted. Over the following monthsAsaro and his colleague Helen Michel worked up to thirty hours at a stretch (“Once youstarted you couldn’t stop,” Asaro explained) analyzing samples, always with the same results.
Tests on other samples—from Denmark, Spain, Franew Zealand, Antarctica—showedthat the iridium deposit was worldwide and greatly elevated everywhere, sometimes by asmuch as five huimes normal levels. Clearly something big and abrupt, and probablycataclysmic, had produced this arresting spike.
After much thought, the Alvarezes cluded that the most plausible explanation—plausible to them, at any rate—was that the Earth had been struck by an asteroid or et.
The idea that the Earth might be subjected to devastating impacts from time to time was notquite as new as it is now sometimes presented. As far back as 1942, a NorthwesternUy astrophysicist named Ralph B. Baldwin had suggested such a possibility in anarticle in Popular Astronomy magazine. (He published the article there because no academicpublisher repared to run it.) And at least two well-known stists, the astronomerErnst ?pik and the chemist and Nobel <bdo></bdo>laureate Harold Urey, had also voiced support for thenotion at various times. Even among paleontologists it was not unknown. In 1956 a professorat on State Uy, M. W. de Laubenfels, writing in the Journal of Paleontology, hadactually anticipated the Alvarez theory by suggesting that the dinosaurs may have bee adeath blow by an impact from space, and in 1970 the president of the AmeriPaleontological Society, Dewey J. McLaren, proposed at the group’s annual ferehepossibility that araterrestrial impact may have been the cause of an earlier event knownas the Frasniain.
As if to underline just how un-he idea had bee by this time, in 1979 aHollywood studio actually produced a movie called Meteor (“It’s five miles wide . . . It’sing at 30,000 m.p.h.—and there’s no place to hide!”) starring Henry Fonda, NatalieWood, Karl Malden, and a very large rock.
So when, in the first week of 1980, at a meeting of the Ameri Association for theAdva of Sce, the Alvarezes annouheir belief that the dinosaur extinhad not taken place over millions of years as part of some slow inexorable process, butsuddenly in a single explosive event, it shouldn’t have e as a shock.
But it did. It was received everywhere, but particularly in the paleontological unity,as an eous heresy.
“Well, you have to remember,” Asaro recalls, “that we were amateurs in this field. Walterwas a geologist specializing in paleomagism, Luis hysicist and I was a nuclearchemist. And now here we were telling paleontologists that we had solved a problem that hadeluded them for over a tury. It’s not terribly surprising that they didn’t embrace itimmediately.” As Luis Alvarez joked: “We were caught practig geology without alise.”
But there was also something much deeper and more fually abhorrent in the impacttheory. The belief that terrestrial processes were gradual had beeal in natural historysihe time of Lyell. By the 1980s, catastrophism had been out of fashion for so long that ithad bee literally unthinkable. For most geologists the idea of a devastating impact was, asEugene Shoemaker noted, “against their stific religion.”
Nor did it help that Luis Alvarez enly ptuous of paleontologists and theirtributions to stifiowledge. “They’re really not very good stists. They’re morelike stamp collectors,” he wrote in the New York Times in an article that stings yet.
Oppos of the Alvarez theory produced any number of alternative explanations for theiridium deposits—for instahat they were geed by prolonged volic eruptions inIndia called the De Traps—and above all insisted that there was no proof that thedinosaurs disappeared abruptly from the fossil record at the iridium boundary. One of themost vigorous oppos was Charles Officer of Dartmouth College. He insisted that theiridium had been deposited by volic a even while g in a neer interviewthat he had no actual evidence of it. As late as 1988 more than half of all Ameripaleontologists tacted in a survey tio believe that the extin of the dinosaurswas in no way related to an asteroid or etary impact.
The ohing that would most obviously support the Alvarezes’ theory was the ohingthey didn’t have—an impact site. Enter Eugene Shoemaker. Shoemaker had an Iowae—his daughter-in-law taught at the Uy of Iowa—and he was familiar withthe Manson crater from his own studies. Thanks to him, all eyes now turo Iowa.
Geology is a profession that varies from place to place. In Iowa, a state that is flat andstratigraphically uful, it tends to be paratively serehere are no Alpine peaks rinding glaciers, no great deposits of oil or preetals, not a hint of a pyroclastic flow.
If you are a geologist employed by the state of Iowa, a big part of the work you do is toevaluate Manure Ma Plans, which all the state’s “animal fi operators”—hog farmers to the rest of us—are required to file periodically. There are fifteen million hogsin Iowa, so a lot of mao manage. I’m not mog this at all—it’s vital and enlightenedwork; it keeps Iowa’s water —but with the best will in the world it’s ly dodginglava bombs on Mount Pinatubo or scrabbling over crevasses on the Greenland ice sheet insearch of a life-bearing quartzes. So we may well imagihe flutter of excitement thatswept through the Ioartment of Natural Resources when in the mid-1980s the world’sgeological attention focused on Manson and its crater.
Tre Hall in Iowa City is a turn-of-the-tury pile of red brick that houses theUy of Iowa’s Earth Sces department and— in a kind of garret—thegeologists of the Ioartment of Natural Resources. No one now remember quitewhen, still less why, the state geologists were placed in an academic facility, but you get theimpression that the space was ceded grudgingly, for the offices are cramped and low-ceilinged and not very accessible. When being shown the way, you half expect to be taken outonto a roof ledge and helped in through a window.
Ray Anderson and Brian Witzke spend their w lives up here amid disordered heapsof papers, journals, furled charts, ay spe stones. (Geologists are a lossfor paperweights.) It’s the kind of space where if you want to find anything—ara chair, acoffee cup, a ringing telephone—you have to move stacks of dots around.
“Suddenly we were at the ter of things,” Anderson told me, gleaming at the memory ofit, when I met him and Witzke in their offices on a dismal, rainy m in June. “It was awonderful time.”
I asked them about Gene Shoemaker, a man who seems to have been universally revered.
“He was just a great guy,” Witzke replied without hesitation. “If it hadn’t been for him, thewhole thing would never have gotten off the ground. Even with his support, it took two yearsto get it up and running. Drilling’s an expensive business—about thirty-five dollars a footback then, more now, and we o go down three thousa.”
“Sometimes more than that,” Anderson added.
“Sometimes more than that,” Witzke agreed. “And at several locations. So you’re talking alot of money. Certainly more than our budget would allow.”
So a collaboration was formed between the Iowa Geological Survey and the U.S.
Geological Survey.
“At least we thought it was a collaboration,” said Anderson, produg a small painedsmile.
“It was a real learning curve for us,” Witzke went on. “There was actually quite a lot of badsce going on throughout the period—people rushing in with results that didn’t alwaysstand up to scrutiny.” One of those moments came at the annual meeting of the AmeriGeophysical Union in 1985, when Glen and C. L. Pillmore of the U.S. GeologicalSurvey annouhat the Manson crater was of the right age to have been involved with thedinosaurs’ extin. The declaration attracted a good deal of press attention but wasunfortunately premature. A more careful examination of the data revealed that Manson wasnot 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 arrivedat a feren South Dakota and found people ing up to them with sympathetic looksand saying: “We hear you lost your crater.” It was the first they khat Izett and the S stists had just announced refined figures revealing that Manson couldn’t after allhave beein crater.
“It retty stunning,” recalls Anderson. “I mean, we had this thing that was reallyimportant and then suddenly we didn’t have it anymore. But even worse was the realizationthat the people we thought we’d been collaborating with hadn’t bothered to share with us theirnew findings.”
“Why not?”
He shrugged. “Who knows? Anyway, it retty good insight into how unattractivesce get when you’re playing at a certain level.”
The search moved elsewhere. By 1990 one of the searchers, Alan Hildebrand ofthe Uy of Arizona, met a reporter from the Houston icle who happeo knowabout a large, unexplained ring formation, 120 miles wide and 30 miles deep, under Mexico’sYu Peninsula at Chicxulub, he city reso, about 600 miles due south of NewOrleans. The formation had been found by Pemex, the Mexi oil pany, in 1952—theyear, tally, that Gene Shoemaker first visited Meteor Crater in Arizona—but thepany’s geologists had cluded that it was voli lih the thinking of the day.
Hildebrand traveled to the site and decided fairly swiftly that they had their crater. By early1991 it had beeablished to nearly everyone’s satisfa that Chicxulub was the impactsite.
Still, many people didn’t quite grasp what an impact could do. As Stephen Jay Gouldrecalled in one of his essays: “I remember harb some strong initial doubts about theefficacy of su event . . . [W]hy should an objely six miles across wreak such havo a pla with a diameter of eight thousand miles?”
vely a natural test of the theory arose when the Shoemakers and Levy discoveredet Shoemaker-Levy 9, which they soon realized was headed for Jupiter. For the first time,humans would be able to witness a ic collision—and witness it very well thanks to thenew Hubble space telescope. Most astronomers, acc to Curtis Peebles, expected little,particularly as the et was not a coherent sphere but a string of twenty-one fragments. “Mysense,” wrote one, “is that Jupiter will swallow these ets up without so much as a burp.”
One week before the impaature ran an article, “The Big Fizzle Is ing,” predigthat the impact would stitute nothing more than a meteor shower.
The impacts began on July 16, 1994, went on for a week and were bigger by far thanah the possible exception of Gene Shoemaker—expected. One fragment, knownas Nucleus G, struck with the force of about six milliooy-five times morethan all the nuclear onry ienucleus G was only about the size of a smallmountain, but it created wounds in the Jovian surface the size of Earth. It was the final blowfor critics of the Alvarez theory.
Luis Alvarez never knew of the discovery of the Chicxulub crater or of the Shoemaker-Levy et, as he died in 1988. Shoemaker also died early. Ohird anniversary of theShoemaker-Levy impact, he and his wife were in the Australian outback, where they wentevery year to searpact sites. On a dirt tra the Tanami Desert—normally ohe emptiest places oh—they came over a></a> slight rise just as another vehicle roag. Shoemaker was killed instantly, his wife injured. Part of his ashes were sent tothe Moon aboard the Lunar Prospector spacecraft. The rest were scattered aroueorCrater.
Anderson and Witzke no longer had the crater that killed the dinosaurs, “but we still hadthe largest and most perfectly preserved impact crater in the mainland Uates,”
Anderson said. (A little verbal dexterity is required to keep Manson’s superlative status. Othercraters are larger—notably, Chesapeake Bay, which was reized as an impact site in1994—but they are either offshore or deformed.) “Chicxulub is buried uwo to threekilometers of limestone and mostly offshore, which makes it difficult to study,” Anderso on, “while Manson is really quite accessible. It’s because it is buried that it is actuallyparatively pristine.”
I asked them how much warning we would receive if a similar hunk of rock was ingtoward us today.
“Oh, probably none,” said Anderson breezily. “It wouldn’t be visible to the naked eye untilit warmed up, and that wouldn’t happen until it hit the atmosphere, which would be about onesed before it hit the Earth. You’re talking about something moving many tens of timesfaster than the fastest bullet. Unless it had been seen by someoh a telescope, and that’sby no means a certainty, it would take us pletely by surprise.”
How hard an impactor hits depends on a lot of variables—angle of entry, velocity andtrajectory, whether the collision is head-on or from the side, and the mass ay of theimpag object, among much else—none of which we know so many millions of yearsafter the fact. But what stists do—and Anderson and Witzke have done—is measurethe impact site and calculate the amount of energy released. From that they work outplausible sarios of what it must have been like—or, more chillingly, would be like if ithappened now.
An asteroid or et traveling at ic velocities would ehe Earth’s atmosphere atsuch a speed that the air beh it couldn’t get out of the way and would be pressed, as ina bicycle pump. As anyone who has used such a pump knows, pressed air grows swiftlyhot, and the temperature below it would rise to some 60,000 Kelvin, or ten times the surfacetemperature of the Sun. In this instant of its arrival in our atmosphere, everything ieor’s path—people, houses, factories, cars—would kle and vanish like cellophane in aflame.
One sed after entering the atmosphere, the meteorite would slam into the Earth’ssurface, 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 a thousand cubieters of rock, earth, and superheated gases. Every living thing within 150 miles thathadn’t been killed by the heat of entry would now be killed by the blast. Radiating outward atalmost 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 wouldbe a flash of blinding light—the brightest ever seen by human eyes—followed an instant to aminute or two later by an apocalyptic sight of unimaginable grandeur: a roiling wall ofdarkness reag high into the heavens, filling aire field of view and traveling atthousands of miles an hour. Its approach would be eerily silent si would be moving farbeyond the speed of sound. Anyone in a tall building in Omaha or Des Moines, say, whoced to look in the right dire would see a bewildering veil of turmoil followed byinstantaneous oblivion.
Within minutes, over aretg from Deo Detroit and enpassing what hadonce been Chicago, St. Louis, Kansas City, the Twin Cities—the whole of the Midwest, inshort—nearly every standing thing would be flattened or on fire, and nearly every living thingwould be dead. People up to a thousand miles away would be knocked off their feet and slicedor clobbered by a blizzard of flying projectiles. Beyond a thousand miles the devastation fromthe blast would gradually diminish.
But that’s just the initial shockwave. No one do more than guess what the associateddamage would be, other than that it would be brisk and global. The impact would almostcertainly set off a of devastatihquakes. Voloes across the globe would beginto rumble and spew. Tsunamis would rise up and head devastatingly for distant shores. Withinan hour, a cloud of blaess would cover the pla, and burning rod other debriswould be pelting down everywhere, setting much of the pla ablaze. It has beeimatedthat at least a billion and a half people would be dead by the end of the first day. The massivedisturbao the ionosphere would knock out unications systems everywhere, sosurvivors would have no idea what was happening elsewhere or where to turn. It would hardlymatter. As one entator has put it, fleeing would meaing a slow death over aquie. The death toll would be very little affected by any plausible relocation effort, sih’s ability to support life would be universally diminished.”
The amount of soot and floating ash from the impad following fires would blot out thesuainly for months, possibly for years, disrupting growing cycles. In 2001 researchers atthe California Institute of Teology analyzed helium isotopes from sediments left from thelater KT impad cluded that it affected Earth’s climate for about ten thousand years.
This was actually used as evideo support the notion that the extin of dinosaurs wasswift and emphatid so it was in geological terms. We only guess how well, orwhether, humanity would cope with su event.
And in all likelihood, remember, this would e without warning, out of a clear sky.
But let’s assume we did see the objeing. What would we do? Everyone assumes wewould send up a nuclear warhead and blast it to smithereens. The idea has some problems,however. First, as John S. Lewis notes, our missiles are not designed for space work. Theyhaven’t the oomph to escape Earth’s gravity and, even if they did, there are no meisms toguide them across tens of millions of miles of space. Still less could we send up a shipload ofspace cowboys to do the job for us, as in the movie Armageddon; we no longer possess arocket 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 anew one because, amazingly, the plans for Saturn launchers were destroyed as part of aNASA houseing exercise.
Even if we did manage somehow to get a warhead to the asteroid and blasted it to pieces,the ces are that we would simply turn it into a string of rocks that would slam into us oer the other in the manner of et Shoemaker-Levy on Jupiter—but with the differe now the rocks would be intensely radioactive. Tom Gehrels, an asteroid hu theUy of Arizona, thinks that even a year’s warning would probably be insuffit totake appropriate a. The greater likelihood, however, is that we wouldn’t see any object—even a et—until it was about six months away, which would be much too late.
Shoemaker-Levy 9 had been orbiting Jupiter in a fairly spianner since 1929, but ittook over half a tury before aiced.
Iingly, because these things are so difficult to co<s>.</s>mpute and must incorporate such asignifit margin of error, even if we knew an object was heading our ouldn’tknow 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 e of uainty.
It would certainly be the most iing few months in the history of the world. And imagihe party if it passed safely.
“So how often does something like the Manson impact happen?” I asked Anderson andWitzke before leaving.
“Oh, about once every million years on average,” said Witzke.
“And remember,” added Anderson, “this was a relatively mi. Do you know howmains were associated with the Manson impact?”
“No idea,” I replied.
“None,” he said, with a strange air of satisfa. “Not one.”
Of course, Witzke and Anderson added hastily and more or less in unison, there wouldhave been terrible devastation auch of the Earth, as just described, and pleteannihilation for hundreds of miles around ground zero. But life is hardy, and when the smokecleared there were enough lucky survivors from every species that none permalyperished.
The good news, it appears, is that it takes an awful lot to extinguish a species. The badnews is that the good news ever be ted on. Worse still, it isn’t actually necessary tolook to space for petrifying danger. As we are about to see, Earth provide plenty of dangerof its own.
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