Francis Bacon captured a key aspect of science when he said that "Truth emerges more readily from error than from confusion."
Science learns from its mistakes. To find them, scientists must criticize, or dissent, at least for a while. Outsiders, not being caught up in the mores and personal relationships of their newly chosen discipline, are in a particularly strong position to dissent from the prevailing view. The best scientists dissent from even their own conclusions, as when Luis invented a new theory every week and (successfully for a while) shot each down in turn, or when Raup tried to "kill the periodicity." Only after they have been unable to falsify their own results do they publish. When scientists initially fail to dissent from their own still tentative conclusions (often by avoiding the obvious, definitive test), they run the risk of dishonoring themselves and forsaking their discipline. The false claims of cold fusion provide the clearest recent example.
Styles of dissent run the gamut from friendly critic to bitter enemy. Although personal relations may suffer, science ultimately cares little about the form and style of dissent as long as some general rules are followed. Nice people and nasty ones alike can finish first, last, or in the middle. Among the rules are these: Criticism is to be based on new evidence or on a better interpretation of the old evidence. Rebuttals are not only to be voiced at professional meetings, they are to be written up and submitted for peer review and publication. Ad hominem attacks are frowned upon. Ideally, opponents share data, microscopes, and outcrops. Blind tests are cheerfully conducted. And so on.
This brings us naturally to the role of Charles Officer, that most vociferous and untiring critic of the Alvarez theory. His opposition culminated in 1996 with publication of his book with Jake Page, The Great Dinosaur Extinction Controversy.' His dogged, constant, and long lasting resistance is bound to tell us something about how science works.
How far, for instance, will a scientist on the losing end of an argument go? Judging from his book with Page, Officer is willing to go so far as to leave science altogether. Officer's and Page's overall position is given away by this astounding statement: "Most of the 'science' performed by the Alvarez camp has been so inexplicably weak, and the response to it so eagerly accepting by important segments of the scientific press, never mind the popular press and the tabloids, that some skeptics have wondered if the entire affair was not, on the impact side, some kind of scam."' They go on to employ a set of stratagems that seem hauntingly familiar; suddenly one realizes that they are the very ploys used by creationists and others who have no platform of logic. They try, for example, the Confident Assertion: "One of the things that did not happen at the K-T boundary was an impact by a gigantic meteorite,"8 and The Strawman: "There was no big dinosaur bone pile . . . that might have resulted from an instantaneous event."' (Scientists have shown that the K-T extinction would not have produced large bone piles.] They resort to the Red Herring: There "is a connection between livestock problems and the demise of the dinosaurs,"10 and plead for equal time: "Between 1991 and 1993 . . . Science published eleven articles favorable to [impact] and two unfavorable."11 They blame the media: "Before long the bias [of Science] was so evident to members of the Earth science community that few even bothered to submit ... a manuscript that espoused a terrestrial cause"12; and they impugn the motives of the pro-impactors: "In degenerating [research] programs . . . theories are fabricated only in order to accommodate known facts." They conclude that the Alvarez theory is "not merely pathological science but dangerous to boot."13
In courtrooms, legislative halls, and debating tournaments, the more determined and skillful an argument on one side, the more the position of the other side is weakened. Even in the face of a mountain of evidence, an adroit defense attorney can see a guilty man set free. It would be reasonable to assume that Officer's long struggle has weakened the Alvarez theory and that, one day, Officer may overthrow Alvarez. But here we find another way in which science differs: Far from weakening the Alvarez theory, Officer's dissent has greatly strengthened it. Officer's papers were accepted and published in respectable journals, requiring the pro-impactors to polish up their thinking and respond. As a result, we now know far more about the geochemistry of iridium than if Officer and others had accepted from the start that it is indeed a marker of impact not found in volcanic rocks. We now know much more firmly that multiple sets of planar deformation features are caused only by impact. Blind tests have been conducted that otherwise would have been deemed a waste of time.
With an irony worthy of Greek tragedy, Officer's tireless, obsessive battle has had just the opposite outcome than he intended; its main effect has been to cause doubters to reserve judgment and to wait for stronger evidence to support impact, which eventually came. Today, hardly anyone other than Officer doubts the existence of the Chicxulub crater, though, as noted, some paleontologists do doubt that it is linked to the K-T mass extinction. Officer's role is different from that of, say, G. K. Gilbert, or from the authorities who opposed continental drift from the 1920s through the 1960s. When those magisters pronounced that terrestrial craters were caused by gas explosions from below, or that continents cannot move, research was shut down for half a century or more. Officer's opposition, and especially his style, made the pro-impactors try all the harder.
WHERE FROM HERE?
Science and evolution both operate as punctuated equilibria. Almost all scientists work to extend and perfect the prevailing paradigm, and continue doing so until a new discovery, often made by accident, requires that the paradigm be reexamined. At first, attempts are made to fit the new discovery in, and often they succeed for a while. But gradually it becomes clear to the more progressive practitioners of a discipline that the old paradigm simply cannot explain enough of the new evidence and must be replaced. The progress of science is then punctuated by the arrival of a new paradigm, which in most cases was developing offline, like a shadow government, ready to step in when needed.
Just after the arrival of a new paradigm, things are muddled and confused. Some questions have been answered but more have been raised. Like species after the punctuation of biological equilibrium, science is now evolving rapidly. It is not always a pretty sight as some continue to hang back while others shoulder in. Because it is hard to know which research directions are apt to be the most fruitful, false leads are followed and dead-end sidings are entered. The old methods and theories prove unable to explicate the new paradigm and new methods have to be invented. The immediate aftermath of the arrival of a new paradigm presents many niches of opportunity into which the nimble, the young turks, and the outsiders can move. (This was the state of physics during the 1930s and 1940s, of which a young turk named Luis Alvarez took full advantage.) In time, these birthing pangs recede, scientists turn to extending and perfecting the new paradigm, and the cycle begins anew.
Earth scientists know that this is the way a paradigm shifts, for between 1966 when plate tectonics arrived and, say, 19'6, when it was fully developed and accepted, we were witnesses. Now, with the Alvarez theory just a decade-and-a-half old and the crater discovered only in the 1990s, geology once again finds itself in a time of great opportunity. If impact has played the broader role hinted at in these chapters, important discoveries may lie just ahead.
What do we know today about the role of meteorite impact? We know that it was the dominant process in the primordial solar system. As the objects that had just condensed from the solar dust cloud collided with each other, sometimes fragmenting and some times adhering, the inner planets were born. For hundreds of millions of years thereafter, impact continued alternately to destroy and to rebuild their surfaces. One giant collision even carved the moon from the earth. The early bombardment was so intense that the surfaces of the inner planets and their satellites melted completely. Nothing escaped the inevitability of impact. Those objects that appear at first glance to have avoided it, for example, certain of Jupiter's moons, turn out to have had recent volcanic activity or to be covered with ice, obscuring the underlying craters. Every object in the solar system has been shaped by myriad collisions. Three decades of research have proven Gene Shoemaker right: Impact is "the most fundamental process."
The impact of comets and asteroids on the earth might not only have destroyed life, it might have delivered it. The K-T boundary clay contains amino acids not found elsewhere on our planet; perhaps the early impacting comets brought with them other building blocks of life that then combined and evolved to colonize Earth. Or, perhaps life developed first on Mars and was brought to Earth by a chunk of rock blasted off the red planet by impact. These are among the exciting possibilities that scientists will be studying over the next few years.
If impact is fundamental in the solar system taken as a whole, Earth could not have escaped. We have discovered about 160 impact craters, of which one—Chicxulub—was formed in the most energetic event in the last billion years of earth history. Even though it is counterintuitive, our intellect requires that we recognize that Earth has been struck many more times than 160; it must have been hit thousands, indeed tens of thousands of times. But where is the evidence of these collisions and their effect on Earth and on life? Could 50 million bombs the size of the one dropped on Hiroshima exploding every ' million years, and larger events less often, have had no effect on life? So far, the evidence is insufficient to answer this question. This contradiction between reason and observation could have one of three explanations, or, more likely, a combination of all of them: First, most of the evidence of impact may have been removed by erosion; second, our methods of detecting impact may be inadequate; or third, we may not have looked systematically enough. This third possibility represents an opportunity.
So far in this story, advances have come about in the traditional way: through the efforts of scientists working alone or in small groups, each following their intellectual curiosity, without an overall strategy. Though many scientists would agree with Al Fischer, who does not like "science by committee," one can still ask whether this style of research is most apt to produce rapid progress in exploring the implications of the Alvarez theory. Given the disparate interests of scientists, and what we now know to be the complexity of the questions, the difficulty of reading the geologic record, and the scarcity of funding, there is a case for focusing resources and proceeding strategically. One idea would be to establish a Center for the Study of Impact and Extinction where scientists from a variety of disciplines could come together. The National Science Foundation funds such centers in other fields on university campuses; models exist and they have proven effective.
What would such a center do? Two lines of research are essential. The greatest obstacle to progress is that the ages of geologic boundaries, extinction horizons, impact craters, and flood basalts are not known with sufficient precision or accuracy to permit firm conclusions. The first need, then, is to improve techniques of age measurement. The argon-argon method is the most precise (most reproducible), but its accuracy (closeness to the true value) can be improved.
Rather than a large number of boundaries and possibly corresponding craters being studied more superficially, a selected few should be dated and explored in depth. Horizons that appear to have corresponding flood basalts should be chosen and the ages of both the basalts and the boundary pinned down precisely and accurately. Perhaps the most immediate payoff would come from precisely dating several impact craters that now appear to be the result of periodic impacts, but where poor age precision leaves an uncertainty. If it could be established with statistical rigor that, say, a dozen craters were periodic, the periodicity of extinction, though not directly proven, would be much more plausible.
The second fruitful direction, suggested by Peter Ward, would complement the first.14 Until now, scientists have started with evidence of impact and searched for the parental crater. This is how Chicxulub was found, but how easy it would have been to miss! Working in the other direction may be more productive: Start with a few of the craters selected for precise age dating, and look for impact and extinction effects at the corresponding levels in the geologic column. Once the age of a crater is pinned down, geologists will know where to look in stratigraphic sections to find the corresponding effects. If, at the predicted level, no impact evidence is found, when geologic techniques have improved enough so that we can be reasonably certain the evidence would have been found had it existed (the flaw now), the K-T event would appear singular and impact would somehow be of lesser import in earth history than we thought. Back to the drawing board. On the other hand, if through such methods the periodicity of cratering could be corroborated, and if three or four craters could be tied to specific extinctions, the Raup-Shoemaker impact-kill curve (see Figure 24) could be roughly calibrated and at least its overall shape determined, giving graphic form to a scientific revolution.
We have seen how a young geologist in Italy, studying something else, decided to bring home for his father a specimen that captured one of the major events in earth history. Thus was launched a scientific partnership that, conjoined with the work of hundreds of proponents and opponents alike, led to the solution of a great mystery. Today we have gone about as far as science can go in corroborating the notion that the impact of a meteorite caused the extinction of the dinosaurs. But as always, answering one set of questions raises others, and we are left pondering the true role of impact. As even its bitterest opponents have to admit, the Alvarez theory has brought geology not only a new set of questions, but a greatly improved set of sampling techniques and analytical methods for answering them. Paleontologists collect much larger samples and subject them to statistical tests. Today geologists know how to find and identify terrestrial craters. These are the hallmarks of a fertile theory.
In 1996, science writer John Horgan published a highly controversial book, The End of Science," in which he argued that such disciplines as physics, cosmology, evolutionary biology, social science, and chaos theory, have run into intellectual cul-de-sacs, are no longer productive, and therefore have come to their natural end. Whether or not one is persuaded by his argument, it is significant that Horgan mentions not a single example from the earth sciences. Far from coming to an end, beginning with plate tectonics in the 1960s, moving on to incorporate the advances of the space age, continuing today with the exploration of the Alvarez theory, and proceeding on tomorrow to determine the true place of impact and the causes of mass extinction, geology is in its golden age.
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