The Flamingo’s Smile (38 page)

We can also extend this theme of continuity, flexibility, and ecumenism to the generation of the argument about nuclear winter within science itself. Working out the details required the combined skills of physicists, meteorologists, chemists, biologists, experts on the mechanics of cratering, on the behavior of suspended particles. I am happy to report that one of the two major inspirations for the TTAPS group came directly from my own field of paleontology, so often viewed as an arcane discipline devoted to events of the distant past without immediate relevance to human life. I have written several essays on the impact theory of the Cretaceous extinction—the exciting idea, now just a few years old but gaining continually in force and evidence, that the extinction of dinosaurs and many other creatures 65 million years ago may have been triggered by the impact of comets or asteroids that struck the earth and left evidence for their bombardment in high levels of iridium, an element of great rarity in indigenous rocks of the earth’s crust but more common in extraterrestrial bodies (see essays 28 and 30).

Luis Alvarez, the great Berkeley physicist and cofounder of the impact theory, has advocated from the start a scenario for extinction based upon a massive dust cloud thrown aloft by the cosmic crash, with subsequent suppression of photosynthesis and plunging temperatures. He also explicitly recognized the parallels between cometary zap and nuclear war (in fact the megatonnage of such an impact greatly exceeds the power of our entire nuclear arsenal). Sagan and his colleagues read the message and applied it directly. Good science also displays its continuity across apparently unrelated disciplines.

The impact potentiated our own evolution; without such a blast, I doubt that we would be here to contemplate nuclear winter. Mammals evolved at about the same time as dinosaurs and lived their first 100 million years as small creatures at the periphery of a world dominated by giant reptiles. If dinosaurs had not become extinct in the Cretaceous bombardment, they presumably would still dominate the earth (as they had for 100 million years, so why not for 65 million more), mammals would have remained as small creatures of ratlike size, and intelligence would not have evolved to create the glories of intellect and the horrors of nuclear holocaust. Is it not a hopeful thought that by recognizing the cause for a key event that inspired our own evolution, we might also contribute, through its direct input in formulating the argument of nuclear winter, to our survival against the greatest threat ever produced by the tree of life against its own fragile continuity.

Postscript

The official Vatican’s statement, drafted at our meeting, has now been published. Its full text appears below.

NUCLEAR WINTER: A WARNING

Nuclear war would include among its immediate consequences the death of a large proportion of the populations in combatant nations. Such a war would represent a catastrophe unprecedented in human history. Subsequent radioactive fallout, weakening of the human immune system, disease, and the collapse of medical and other civil services would threaten large numbers of survivors.

We must now issue an additional warning: newly-recognized effects of nuclear war on the global climate indicate that longer-term consequences might be as dire as the prompt effects, if not worse.

In a nuclear war, weapons exploded near the ground would inject large quantities of dust into the atmosphere, and those exploded over cities and forests would suddenly generate enormous amounts of sooty smoke from the resulting fires. The clouds of fine particles would soon spread throughout the Northern Hemisphere, absorbing and scattering sunlight and thus darkening and cooling the earth’s surface. Continental temperatures could fall rapidly—well below freezing for months, even in summertime—creating a “nuclear winter.” This would happen even with wide variations in the nature and extent of nuclear war.

We have only recently become aware of how severe the cold and the dark might be, especially as a consequence of intense and numerous fires ignited by nuclear explosions, and from attendant changes in atmospheric circulation. This would produce a profound additional assault upon surviving plants, animals and humans. Agriculture, at least in the Northern Hemisphere, could be severely damaged for a year or more, causing widespread famine.

Calculations show that the dust and smoke may well spread to the tropics and to much of the Southern Hemisphere. Thus non-combatant nations, including those far from the conflict, could be severely afflicted. Such nations as India, Brazil, Nigeria, and Indonesia could be struck by unparalleled disaster, without a single bomb exploding on their territories.

Moreover, nuclear winter might be triggered by a relatively small nuclear war, involving only a minor fraction of the present global strategic arsenals, provided that cities are targeted and burned. Even if a “limited” nuclear war were initiated in a manner intended to minimize such effects, it would likely escalate to the massive use of nuclear weapons, as the Pontifical Academy of Sciences stressed in its earlier “Declaration on Prevention of Nuclear War” (1982).

The general results seem to be valid over a wide range of plausible conditions, and over wide variations in the character and extent of a nuclear war. However, there are still uncertainties in the present evaluations, and there are effects which have not yet been studied. Therefore, additional scientific work and continuing critical scrutiny of methods and data are clearly required. Unanticipated further dangers from nuclear war cannot be excluded.

Nuclear winter implies a vast increase in human suffering, including nations not directly involved in the war. A large proportion of humans who survive the immediate consequences of nuclear war would most likely die from freezing, starvation, disease, and, in addition, the effects of radiation. The extinction of many plant and animal species can be expected, and, in extreme cases, the extinction of most non-oceanic species might occur. Nuclear war could thus carry in its wake a destruction of life unparalleled at any time during the tenure of humans on Earth, and might therefore imperil the future of humanity.

VULCAN, THE ROMAN GOD OF FIRE
, bestowed his name upon a planet for a few years during the nineteenth century. Appropriately situated in the hottest spot of our immediate heavens, between Mercury and the sun, this putative planet emerged because Newtonian science knew no other way to produce (by gravitational pull) the slight irregularity that had been measured in Mercury’s orbit. Since Vulcan had to exist, and since theory can exert such a remarkable effect upon observation, several sightings were actually reported. We now understand that gravitation is Einsteinian, not perfectly Newtonian, and equations of relativity adequately explain the perturbations of Mercury without an additional disturbing body. Deprived of its theoretical necessity, Vulcan quietly disappeared.

No scientific activity teeters more precariously on the precipice between bravery and foolishness than descriptions of unobserved objects justified only by their necessity in theory. The audacious can even take a firmer step toward perdition or renown by conferring a formal name upon their hypothetical entity. What can a friendly bystander say about such a strategy? We can formulate no general rules for success; as Nick the Greek might say, “ya win some, ya lose some.” The proponents of Vulcan lost big, but others have triumphed in the same game.

Ernst Haeckel, Germany’s leading evolutionist in Darwin’s day, drew a hypothetical lineage of human evolution thirty years before Eugene Dubois discovered the first transitional fossils. On this tree,
Homo sapiens
reached back to a less worthy predecessor named
Homo stupidus
—a hypothetical cretin itself descended from the true missing link joining apes and humans. Haeckel had no fossils, but he did have a name. He called this putative ancestor
Pithecanthropus alalus
, or the ape-man who could not speak. But Haeckel won, where the Vulcanophiles met defeat. So accurate were Haeckel’s major predictions—particularly his claim that our immediate ancestor would walk fully erect but possess a brain far smaller than ours—that Dubois willingly accepted his name, christening the first human fossils
Pithecanthropus erectus
(the specimens from Java now called
Homo erectus
).

In April 1984, inspired by a new theory for the cause of mass extinctions, several scientists christened another unobserved member of our solar system. The sun, they proposed, has a previously unrecognized companion star, revolving in an eccentric orbit and now at a maximal distance of more than two light-years (hence, at its small mass and low luminosity, so barely discernible, even with the most powerful telescopes, that we would easily and forever miss it unless searching directly). They also—why not go whole hog while you’re at it—proposed a name for the sun’s hypothetical companion. They have called it Nemesis (I shall explain why in a moment) to honor the Greeks’ personification of righteous anger in the form of a goddess. “We worry,” they wrote, “that if the companion is not found, this paper will be our nemesis” (Marc Davis, Piet Hut, and Richard A. Muller, see bibliography. Daniel P. Whitmire and Albert A. Jackson IV independently postulated the existence of Nemesis in the same issue of
Nature
).

The prediction of Nemesis culminates a long series of disparate discoveries and conjectures, spanning more than a century but gathering considerable steam in the past few months. I have discussed each item, often many times, during a decade of essays. Their current conjunction and synthesis either marks the most exciting event in my profession of paleontology during my lifetime or just another mistake made by those fallible mortals known as scientists. (I now have ten pounds riding on excitement with a skeptical English colleague.) With my lead time of three months
^*
and the spate of preemptive articles in newspapers and magazines produced more quickly, I would be performing no service in presenting a straight exposition of the theory itself. I wish, instead, to explain why this new theory of mass extinction might be so vitally important in altering our basic conception of the causes of pattern in life’s history. I also want to end with a little gloss upon the theory itself—a plea to potential spotters that they name our companion Siva, not Nemesis, both to express the ecumenical spirit of science at its best and to recognize an almost devastating match between the proposed role of a solar companion in mass extinction and the attributes of this Eastern god of destruction. But first, let me list the primary events now coalescing into a new view of mass extinction.

1. Geologists have known for nearly two centuries that extensive extinctions, affecting life in a wide range of environments, have occurred sporadically and rapidly many times during the past 600 million years. Our geological time scale depends upon these mass extinctions since they set the boundaries of major divisions. My standard response to generations of student groans (at the imposed necessity of memorizing all those funny names from Cambrian to Pleistocene) reminds my charges that they are not learning capricious words for the arbitrary division of continuous time, but rather the dates of major events in the history of life.
   
2. Theories of mass extinction would fill a book thick enough to prop any junior to adult height at the dinner table. But an impasse broke some five years ago, when high levels of iridium in rocks at the Cretaceous-Tertiary boundary (dinosaur doomsday) provided the first solid evidence for coincidence between extraterrestrial impact and times of extinction (see essay 25 in
   Hen’s Teeth and
   Horse’s Toes
   ). Iridium is a heavy, unreactive element, and the earth’s original supply presumably sank into its interior when our planet melted and differentiated some 4 billion years ago. Iridium in surface rocks arrives largely from extraterrestrial sources—asteroids, meteorites, and comets. Unless, of course, the earth’s original iridium can rise from the interior in volcanic eruptions—the only serious challenge proposed against the impact theory.
   
3. Luis Alvarez, Walter Alvarez, Frank Asaro, and Helen Michel proposed that a large asteroid, some ten kilometers in diameter, struck the earth and dumped the iridium some 65 million years ago. They based their suggestion on enhanced iridium in three sites, all for one extinction. Paleontological reactions ranged initially from skepticism to derision (I take considerable pride, in a career liberally studded with error, in my iconoclastic original enthusiasm). Since then, the tenuous base of initial evidence has been greatly strengthened. Enhanced iridium has been found throughout the world in more than fifty localities right at the Cretaceous-Tertiary boundary, from terrestrial sediments to deep-sea cores. Iridium has also been discovered, with varying degrees of confidence, in rocks marking four or five other episodes of mass extinction.
   
4. David Raup and Jack Sepkoski, working from extensive compilations of the life and death times for fossil families, found a 26-million-year periodicity in extinctions during the past 225 million years (see essay 15). (This cyclicity had not been noted before because the smallest of these extinctions could not be separated from ordinary background levels before Sepkoski compiled his more extensive and refined data.)
   
5. Walter Alvarez and Richard A. Muller found a periodicity, similar in timing and spacing (28.4 million years), to the Raup-Sepkoski extinction peaks, for well-dated impact craters on earth with diameters in excess of ten kilometers. Since such craters are rare (fewer than twenty), conclusions must be tentative, but the coincidence of two data sets—neither presumed in the past either to show cyclicity or (for that matter) to have anything to do with each other—is (to say the least) suggestive.
   
6. So far, so solid. The rest is productive speculation about mechanisms: Cyclicity undermined the Alvarez asteroid (good science is self-corrective). Asteroidal impacts, as we understand them, can only occur at random when a so-called Apollo object (an asteroid with an orbit eccentric enough to traverse our part of the sky during its wanderings) strikes the earth. What extraterrestrial object could bring in iridium but also hit the earth with consistent rhythm? Thought shifted to comets.
   
7. Second-level speculation: Billions of comets circle the sun in an envelope called the Oort cloud and located well beyond the orbit of Pluto. Gravitational disturbance of this cloud might alter cometary orbits and send large numbers hurtling into the space of the inner planets. Some would then strike the earth.
   
8. Third-level speculation: What could so perturb the Oort cloud at a 26-million-year periodicity? Various suggestions have emerged. Oscillations of the solar system with respect to the plane of our galaxy (bringing the Oort cloud in and out of contact with interstellar clouds of dust and gas) have been proposed, but the timing and length of these excursions—a cycle of some 33 million years—fit the extinction and cratering data poorly. A solar companion, on an orbit so eccentric that it perturbs the Oort cloud only on its closest approach, seems to work in principle. Such a notion sounds, I freely confess, like science fiction of the lowest order, but the idea must be taken most seriously, for it obeys the cardinal criterion of fruitful science. It is plausible in theory and testable in practice (see essay 28). We can scan the skies and hope to know—a gamble well worth taking (even for low probability), given the immense intellectual reward of potential success. Piet Hut told me that we should have a 50 percent chance of finding the companion within three years, if it exists. And, oh yes, don’t worry. Our companion is now at its maximal distance; the Oort cloud won’t be jolted for another 13 million years or so.
   

Cometary showers and shrouds of dust must titillate anyone’s fancy, but their fascination for paleontologists lies not with the wham-bam of the western movie scenario, but in a profound implication that we must face squarely and that may fundamentally alter our favorite principle for explaining life’s history. We may identify two extreme (and contrasting) positions as guides for interpreting life’s pattern in time. (All astute paleontologists recognize that the truth lies somewhere in between, but I wish to argue that the first has been favored as a kind of controlling metaphor, while new views on mass extinction suggest a far greater role for the second.)

The first holds that competition among species drives the history of life forward and specifies its steady changes. Even if environments were perfectly constant, evolution would continue as organisms struggle (literally or figuratively) with others in the race for life. You don’t necessarily get anywhere (measured by triumph over others) because everyone else is struggling too, but the net result is a kind of upward relay preserving balances among competitors as all struggle for temporary advantages. Paleontologist Leigh Van Valen has codified this model for life’s history as the “Red Queen” hypothesis in honor of Alice’s compatriot (in
Through the Looking Glass
), who had to keep running all the time just to stay in the same place.

The Red Queen has been our dominant model for life’s history. It is Darwin’s own controlling metaphor of the wedge recast for the fullness of time:

Nature, in other words, is always full (or near equilibrium, in technical parlance). One form can gain a space only by pushing another out (“wedging,” in Darwin’s words). The metaphor of the wedge underlies and supports our conventional view of life’s order: Creatures strive to improve themselves; life moves steadily upward although no one gets permanently ahead; order rules as the predictable struggle of individuals translates to patterns of increasing complexity and diversity. Marx was not far wrong when he remarked of Darwin’s system that it resembled Hobbes’s
bellum omnium contra omnes
(the war of all against all) imposed upon nature.

The second, or minority, view holds that no internal dynamic drives life forward. If environments did not change, evolution might well grind to a virtual halt. At a high level of paleontological resolution (if not among the bugs and birds in my garden), species pass their lives in general independence, as Longfellow’s “Ships that pass in the night…. Only a signal shown and a distant voice in the darkness.” Their primary “struggles” are with changing climates, geologies, and geographies, not with each other. (Competition then becomes a sporadic and local interaction, smoothing and shaping the edges of life’s order, but not acting as its driving force.)

In this view, external triggers of changing environment must drive the history of life forward. But they drive it in unconventional directions: Where can we find the upward advance that we seek so assiduously (to put ourselves on top of a struggling mass) if life only tracks a capriciously changing environment? Where can we locate predictable order at all if the primary environmental triggers are periodic cometary showers?

To cite a specific example contrasting the two views and their differing implications, I restudied (with C. Brad Calloway, see bibliography) the standard textbook case of wedging on a grand scale: the interaction of clams and brachiopods through time. These major groups of marine invertebrates look superficially similar: both cover their body with two shells and most species either attach to the sea bottom or, with limited mobility, burrow into sediments. But clams have a more complex anatomy and are conventionally ranked higher in the old Procrustean classifications that forced the bush of life into linear order. Clams also dominate many marine faunas today, while brachiopods are relatively inconspicuous; our early fossil record, however, is replete with brachiopods and depauperate in clams. Thus, we have all the ingredients for a classic tale of gradual competitive replacement by wedging—superior clams, step by step, force brachiopods out of their limited, mutual environment. Calloway and I gathered a compendium of statements, spanning more than a century, and all citing clams and brachiopods as the classic case of progress in life’s history by competitive exclusion.