A short history of nearly everything (27 page)

Alvarez knew that a colleague of his at the Lawrence Berkeley Laboratory in California, Frank Asaro, had developed a technique for measuring very precisely the chemical composition of clays using a process called neutron activation analysis. This involved bombarding samples with neutrons in a small nuclear reactor and carefully counting the gamma rays that were emitted; it was extremely finicky work. Previously Asaro had used the technique to analyze pieces of pottery, but Alvarez reasoned that if they measured the amount of one of the exotic elements in his son’s soil samples and compared that with its annual rate of deposition, they would know how long it had taken the samples to form. On an October afternoon in 1977, Luis and Walter Alvarez dropped in on Asaro and asked him if he would run the necessary tests for them.

It was really quite a presumptuous request. They were asking Asaro to devote months to making the most painstaking measurements of geological samples merely to confirm what seemed entirely self-evident to begin with—that the thin layer of clay had been formed as quickly as its thinness suggested. Certainly no one expected his survey to yield any dramatic breakthroughs.

“Well, they were very charming, very persuasive,” Asaro recalled in an interview in 2002. “And it seemed an interesting challenge, so I agreed to try. Unfortunately, I had a lot of other work on, so it was eight months before I could get to it.” He consulted his notes from the period. “On June 21, 1978, at 1:45 p.m., we put a sample in the detector. It ran for 224 minutes and we could see we were getting interesting results, so we stopped it and had a look.”

The results were so unexpected, in fact, that the three scientists at first thought they had to be wrong. The amount of iridium in the Alvarez sample was more than three hundred times normal levels—far beyond anything they might have predicted. Over the following months Asaro and his colleague Helen Michel worked up to thirty hours at a stretch (“Once you started you couldn’t stop,” Asaro explained) analyzing samples, always with the same results. Tests on other samples—from Denmark, Spain, France, New Zealand, Antarctica—showed that the iridium deposit was worldwide and greatly elevated everywhere, sometimes by as much as five hundred times normal levels. Clearly something big and abrupt, and probably cataclysmic, had produced this arresting spike.

After much thought, the Alvarezes concluded that the most plausible explanation—plausible to them, at any rate—was that the Earth had been struck by an asteroid or comet.

The idea that the Earth might be subjected to devastating impacts from time to time was not quite as new as it is now sometimes presented. As far back as 1942, a Northwestern University astrophysicist named Ralph B. Baldwin had suggested such a possibility in an article inPopular Astronomy magazine. (He published the article there because no academic publisher was prepared to run it.) And at least two well-known scientists, the astronomer Ernst Öpik and the chemist and Nobel laureate Harold Urey, had also voiced support for the notion at various times. Even among paleontologists it was not unknown. In 1956 a professor at Oregon State University, M. W. de Laubenfels, writing in theJournal of Paleontology , had actually anticipated the Alvarez theory by suggesting that the dinosaurs may have been dealt a death blow by an impact from space, and in 1970 the president of the American Paleontological Society, Dewey J. McLaren, proposed at the group’s annual conference the possibility that an extraterrestrial impact may have been the cause of an earlier event known as the Frasnian extinction.

As if to underline just how un-novel the idea had become by this time, in 1979 a Hollywood studio actually produced a movie calledMeteor (“It’s five miles wide . . . It’s coming at 30,000 m.p.h.—and there’s no place to hide!”) starring Henry Fonda, Natalie Wood, Karl Malden, and a very large rock.

So when, in the first week of 1980, at a meeting of the American Association for the Advancement of Science, the Alvarezes announced their belief that the dinosaur extinction had not taken place over millions of years as part of some slow inexorable process, but suddenly in a single explosive event, it shouldn’t have come as a shock.

But it did. It was received everywhere, but particularly in the paleontological community, as an outrageous heresy.

“Well, you have to remember,” Asaro recalls, “that we were amateurs in this field. Walter was a geologist specializing in paleomagnetism, Luis was a physicist and I was a nuclear chemist. And now here we were telling paleontologists that we had solved a problem that had eluded them for over a century. It’s not terribly surprising that they didn’t embrace it immediately.” As Luis Alvarez joked: “We were caught practicing geology without a license.”

But there was also something much deeper and more fundamentally abhorrent in the impact theory. The belief that terrestrial processes were gradual had been elemental in natural history since the time of Lyell. By the 1980s, catastrophism had been out of fashion for so long that it had become literally unthinkable. For most geologists the idea of a devastating impact was, as Eugene Shoemaker noted, “against their scientific religion.”

Nor did it help that Luis Alvarez was openly contemptuous of paleontologists and their contributions to scientific knowledge. “They’re really not very good scientists. They’re more like stamp collectors,” he wrote in theNew York Times in an article that stings yet.

Opponents of the Alvarez theory produced any number of alternative explanations for the iridium deposits—for instance, that they were generated by prolonged volcanic eruptions in India called the Deccan Traps—and above all insisted that there was no proof that the dinosaurs disappeared abruptly from the fossil record at the iridium boundary. One of the most vigorous opponents was Charles Officer of Dartmouth College. He insisted that the iridium had been deposited by volcanic action even while conceding in a newspaper interview that he had no actual evidence of it. As late as 1988 more than half of all American paleontologists contacted in a survey continued to believe that the extinction of the dinosaurs was in no way related to an asteroid or cometary impact.

The one thing that would most obviously support the Alvarezes’ theory was the one thing they didn’t have—an impact site. Enter Eugene Shoemaker. Shoemaker had an Iowa connection—his daughter-in-law taught at the University of Iowa—and he was familiar with the Manson crater from his own studies. Thanks to him, all eyes now turned to Iowa.

Geology is a profession that varies from place to place. In Iowa, a state that is flat and stratigraphically uneventful, it tends to be comparatively serene. There are no Alpine peaks or grinding glaciers, no great deposits of oil or precious metals, 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 to evaluate Manure Management Plans, which all the state’s “animal confinement operators”—hog farmers to the rest of us—are required to file periodically. There are fifteen million hogs in Iowa, so a lot of manure to manage. I’m not mocking this at all—it’s vital and enlightened work; it keeps Iowa’s water clean—but with the best will in the world it’s not exactly dodging lava bombs on Mount Pinatubo or scrabbling over crevasses on the Greenland ice sheet in search of ancient life-bearing quartzes. So we may well imagine the flutter of excitement that swept through the Iowa Department of Natural Resources when in the mid-1980s the world’s geological attention focused on Manson and its crater.

Trowbridge Hall in Iowa City is a turn-of-the-century pile of red brick that houses the University of Iowa’s Earth Sciences department and—way up in a kind of garret—the geologists of the Iowa Department of Natural Resources. No one now can remember quite when, still less why, the state geologists were placed in an academic facility, but you get the impression that the space was conceded grudgingly, for the offices are cramped and low-ceilinged and not very accessible. When being shown the way, you half expect to be taken out onto a roof ledge and helped in through a window.

Ray Anderson and Brian Witzke spend their working lives up here amid disordered heaps of papers, journals, furled charts, and hefty specimen stones. (Geologists are never at a loss for paperweights.) It’s the kind of space where if you want to find anything—an extra chair, a coffee cup, a ringing telephone—you have to move stacks of documents around.

“Suddenly we were at the center of things,” Anderson told me, gleaming at the memory of it, when I met him and Witzke in their offices on a dismal, rainy morning in June. “It was a wonderful 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, the whole thing would never have gotten off the ground. Even with his support, it took two years to get it up and running. Drilling’s an expensive business—about thirty-five dollars a foot back then, more now, and we needed to go down three thousand feet.”

“Sometimes more than that,” Anderson added.

“Sometimes more than that,” Witzke agreed. “And at several locations. So you’re talking a lot 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 wethought 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 U.S. 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 the first they knew 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 anymore. 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 theHouston Chronicle who happened to know about a large, unexplained ring formation, 120 miles wide and 30 miles deep, under Mexico’s Yucatán Peninsula at Chicxulub, near the city of Progreso, about 600 miles 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 traveled 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?”

Conveniently a natural test of the theory arose 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 July 16, 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 megatons—seventy-five times more than 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 Shoemaker-Levy impact, 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. Part 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 an impact site in 1994—but they are either offshore or deformed.) “Chicxulub is buried under two to three kilometers 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.”