The Flamingo’s Smile (37 page)

The impact story, on the other hand, has a sound basis in evidence. It can be tested, extended, refined and, if wrong, disproved. The Alvarezes did not just construct an arresting guess for public consumption. They proposed their hypothesis after laborious geochemical studies with Frank Asaro and Helen Michel had revealed a massive increase of iridium in rocks deposited right at the time of extinction. Iridium, a rare metal of the platinum group, is virtually absent from indigenous rocks of the earth’s crust; most of our iridium arrives on extraterrestrial objects that strike the earth.

The Alvarez hypothesis bore immediate fruit. Based originally on evidence from two European localities, it led geochemists throughout the world to examine other sediments of the same age. They found abnormally high amounts of iridium everywhere—from continental rocks of the western United States to deep sea cores from the South Atlantic.

Cowles proposed his testicular hypothesis in the mid-1940s. Where has it gone since then? Absolutely nowhere, because scientists can do nothing with it. The hypothesis must stand as a curious appendage to a solid study of alligators. Siegel’s overdose scenario will also win a few press notices and fade into oblivion. The Alvarezes’ asteroid falls into a different category altogether, and much of the popular commentary has missed this essential distinction by focusing on the impact and its attendant results, and forgetting what really matters to a scientist—the iridium. If you talk just about asteroids, dust, and darkness, you tell stories no better and no more entertaining than fried testicles or terminal trips. It is the iridium—the source of testable evidence—that counts and forges the crucial distinction between speculation and science.

The proof, to twist a phrase, lies in the doing. Cowles’s hypothesis has generated nothing in thirty-five years. Since its proposal in 1979, the Alvarez hypothesis has spawned hundreds of studies, a major conference, and attendant publications. Geologists are fired up. They are looking for iridium at all other extinction boundaries. Every week exposes a new wrinkle in the scientific press. Further evidence that the Cretaceous iridium represents extraterrestrial impact and not indigenous volcanism continues to accumulate. As I revise this essay in November 1984 (this paragraph will be out of date when the book is published), new data include chemical “signatures” of other isotopes indicating unearthly provenance, glass spherules of a size and sort produced by impact and not by volcanic eruptions, and high-pressure varieties of silica formed (so far as we know) only under the tremendous shock of impact.

My point is simply this: Whatever the eventual outcome (I suspect it will be positive), the Alvarez hypothesis is exciting, fruitful science because it generates tests, provides us with things to do, and expands outward. We are having fun, battling back and forth, moving toward a resolution, and extending the hypothesis beyond its original scope (see essay 30 for some truly wondrous extensions).

As just one example of the unexpected, distant cross-fertilization that good science engenders, the Alvarez hypothesis made a major contribution to a theme that has riveted public attention in the past few months—so-called nuclear winter (see next essay). In a speech delivered in April 1982, Luis Alvarez calculated the energy that a ten-kilometer asteroid would release on impact. He compared such an explosion with a full nuclear exchange and implied that all-out atomic war might unleash similar consequences.

This theme of impact leading to massive dust clouds and falling temperatures formed an important input to the decision of Carl Sagan and a group of colleagues to model the climatic consequences of nuclear holocaust. Full nuclear exchange would probably generate the same kind of dust cloud and darkening that may have wiped out the dinosaurs. Temperatures would drop precipitously and agriculture might become impossible. Avoidance of nuclear war is fundamentally an ethical and political imperative, but we must know the factual consequences to make firm judgments. I am heartened by a final link across disciplines and deep concerns—another criterion, by the way, of science at its best
^*
: A recognition of the very phenomenon that made our evolution possible by exterminating the previously dominant dinosaurs and clearing a way for the evolution of large mammals, including us, might actually help to save us from joining those magnificent beasts in contorted poses among the strata of the earth.

A GOLDEN BAND
of mosaics rims the interior of Michelangelo’s dome in Saint Peter’s Basilica at the Vatican. It is emblazoned with that ultimate geological pun, Christ’s words to Peter, taken ever since as the justification for papal supremacy and continuity.
Tu es Petrus, et super hane petram aedificabo ecclesiam meam
, “Thou art Peter, and upon this rock I will build my church (Matthew 16:18).” In Latin, and in other languages of Christ’s time, Peter’s name means rock (
petra
)—so Christ appointed his first pope by name and perhaps not without a touch of humor. (It’s none of my business, of course, but I have always regarded Peter—the man who denied Christ three times, and then tried to slink out of Rome until Christ reappeared and responded with gentle admonition to his “
Domine, quo vadis?
”—as a fairly weak character to assume such a weighty responsibility.) In any case, the words in golden mosaics symbolize one of the great continuities in our fickle and ephemeral history—an institution (the papacy) that can trace its lineage for two millennia.

There is no city quite like Rome, and no institution quite like the Catholic church, for appreciating continuity—that elusive property that a paleontologist like myself must deem of intrinsic and inestimable value. If subtle tuning to deep human needs and feelings represents the best formula for continuity, then the Church of Rome wins this outsider’s plaudits. At the beautiful Church of Santa Maria in Trastevere, begun in the third century, boys play soccer in the adjoining square at dusk. As the day fades, they move into the lighted portico, under wonderful mosaics of the Virgin, and continue their game admidst the tombs of early Christians. The sacred and the profane must mix.

In the Casina Pio Quatro (Pius IV’s palace) on the grounds of the Vatican, I met in January 1984, the beginning of Orwell’s year, with twenty scientists from eight nations to draft a statement on “nuclear winter” that the pope might use in his speeches against nuclear war. Pius IV was a sixteenth-century pope of the powerful Medici family. His house is a Roman pleasure palace, surrounded by grottoes and terraces emblazoned with statues and bas-reliefs of Roman youths in various postures of play and merriment. The ceilings are painted with swirling designs of imaginative creatures and rather frank symbols of sex and fertility. Cherubs hold aloft the six-balled Medici shield, the symbol of temporal power, with its title befitting a worldly monarch, Pius IIII Pontifex Optimus Maximus. Here and there, almost as an afterthought, a biblical scene—Christ’s baptism by John, for example—fills a space amidst the Roman motifs. Again, sacred and profane, spiritual and temporal, pleasure and contemplation—all packaged into one artistic unity, a symbol of continuity that incorporates the past and recognizes human realities of the present.

I was in Rome to discuss continuity on the grandest scale. A series of studies, performed by independent groups of scientists in several nations and checked and confirmed by leaders in the various disciplines involved, seem to be converging (despite many remaining uncertainties) upon a troubling conclusion. For all prognoses about the horrors of nuclear war, we have previously missed an important theme that makes the prospect of such a holocaust even more unthinkable. We have explored the immediate consequences of blast and fallout, but we have not appreciated the longer-term effects upon climate (months to years) produced because major explosions loft clouds of dust and soot into the atmosphere. Under a range of plausible circumstances, a pall of particles might blanket the earth, bringing sub-zero temperatures to mid-latitude summers and enveloping the earth in such darkness that agriculture might fail completely. This nuclear winter raises, for the first time, the chilling prospect that a major war might not only debilitate and decimate, bringing unparalleled human suffering in its wake, but might also lead to the total and irrevocable extinction of many plant and animal species. We humans are a hardy and well-dispersed lot, but even the possibility of our own disappearance in the aftermath of nuclear winter’s worst scenario cannot be totally excluded.

Why should we be so concerned about extinction? The appalling destruction of nuclear war is enough to contemplate without this added dimension. I could offer a set of “objective” reasons. Some are practical. Corn, our most important crop, will be in trouble if we lose teosinte, its wild grassy ancestor with a limited geographical and ecological distribution in Central and South America. Teosinte hybridizes with corn (see essay 24) and forms a major reserve for the genetic variability that all species require for maintenance and evolutionary flexibility. Other reasons are more frankly aesthetic. It would be an impoverished and bleak world indeed if we encountered nothing but humans and a rat or cockroach now and again. But, for this column, which I present more as a musing on continuity than a technical account of nuclear winter, I wish to emphasize a highly personal, moral argument (not subject to proof but only to simple statement, deeply felt) that flows from my own career as a paleontologist, a student of that greatest of all natural continuities, the genealogy of life on earth.

We now have evidence, in fossils of simple cells and the mats of sediment that aggregates of these cells trap and bind, that life on earth arose at least 3.5 billion years ago. It has, since then, extended upward in time, in unbroken continuity to the present. We can all, quite literally, from moss to mayfly to hippopotamus, trace our ancestry all the way back to these beginnings. The tree is an accurate metaphor for life’s history; the tip of each current twig (we humans are one) flows back through branches ever wider and sturdier to the common trunk of original cells nearly 4 billion years old.

Each extinction permanently removes a bit of this patrimony; each irrevocable death of a species expunges not merely a bit of current protoplasm but a unique pathway of history maintained for 4 billion years. Each extinction is a breach of continuity on the grandest scale. Of course, from a geological perspective measured in millions of years, extinction is inevitable, even necessary for maintaining a vigorous tree of life. We may also argue, both in the abstract and for life’s actual history, that an occasional catastrophic episode of mass extinction opens new evolutionary possibilities by freeing ecological space in a crowded world.

But these geological scales are not appropriate for contemplating our own life and its immediate meaning. The potentially beneficial effect of a mass extinction on life’s unpredictable rebound 10 million years down the road cannot speak to the significance of our own twig on life’s tree—and we do not display cosmic vanity, but merely appropriate self-interest, when we choose to nurture and defend this particular little branch.

Ours is a small twig indeed, but remember that it runs back, by myriad branches, through 4 billion years to the central trunk itself. Our origin in Africa, and our subsequent spread throughout the world, form a complex and compelling tale expressing our continuity with the entire history of life. If we extirpate this twig directly by nuclear winter, or lose so many other twigs that our own eventually withers away, then we have canceled forever the most peculiar and different, unplanned experiment ever generated among the billions of branches—the origin, via consciousness, of a twig that could discover its own history and appreciate its continuity.

Some people, who have never extricated themselves from the chain of being (see essays 17–19), and who view life’s history as a tale of linear progress leading predictably to the evolution of consciousness, might be less troubled (in some abstract sense) by our potential self-removal. After all, evolution moves toward complexity and consciousness. If not us, then some other surviving branch will enter the stream and eventually give intelligence a second chance. And if not here, then elsewhere in a populated universe, for nature’s laws do not vary from place to place.

As a student of life’s history, and as a man who has tried hard to separate cultural prejudice and psychological hope from the story that fossils are trying to tell us, I have reached quite a different conclusion, shared, I think, by most professional colleagues: consciousness is a quirky evolutionary accident, a product of one peculiar lineage that developed most components of intelligence for other evolutionary purposes (see essay 27). If we lose its twig by human extinction, consciousness may not evolve again in any other lineage during the 5 billion years or so left to our earth before the sun explodes. Through no fault of our own, and by dint of no cosmic plan or conscious purpose, we have become, by the power of a glorious evolutionary accident called intelligence, the stewards of life’s continuity on earth. We did not ask for this role, but we cannot abjure it. We may not be suited for such responsibility, but here we are. If we blow it (quite literally), we will permanently rupture a continuity of eons that dwarfs our own puny history to geological insignificance, but that we nonetheless now control. I cannot imagine anything more vulgar, more hateful, than the prospect that a tiny twig with one peculiar power might decimate a majestic and ancient tree, whose continuity stretches back to the dawn of earth’s time and whose trunk and branches house so many thousand prerequisites to the twig’s existence.

The argument for nuclear winter has several sources and parents. But it came to prominence toward the end of 1983 primarily through the work of a team with the appropriate acronym of TTAPS—R.P. Turco, O.B. Toon, T.P. Ackerman, J.B. Pollack, and Carl Sagan. Climatic modeling represents an unfamiliar style of science, quite different from the schoolboy stereotype of simple experiment with clear prediction and unambiguous test. We must deal, instead, with a score of variables whose values we cannot specify exactly and whose interactions are largely unknown since the experiment, thank God, has not been tried. How much dust and soot goes up; does it spread to a homogeneous layer or does it leave holes for intermittent sunlight; does it spread to the Southern Hemisphere and, if so, how intensely; where in the atmosphere do dust and soot lodge and how long will they stay before rains scavenge the particles and bring them to earth; how cold will it get; how long will the effects last? I could go on forever but will stop here. Moreover, these are only the first-order questions about unknown immediate results. What about interactions among the effects, for such “synergisms” often are, in technical parlance, nonadditive—that is, bad plus bad may not equal twice as bad, but many times worse. Radiation, for example, weakens the human immune system. It also engenders high mutation rates that might lead to the evolution of a particularly virulent agent of disease. The interaction of this new disease vector with human bodies of markedly reduced resistance might produce a pandemic far greater in effect than any prediction, based on components considered separately, could envision.

In the face of these difficulties and uncertainties, the TTAPS team proceeded by specifying the most reasonable range of values for each effect and by modeling hundreds of possible scenarios to obtain some sense of plausible scope. Major variations depend largely upon differing behaviors and amounts of dust and soot. In short, and with some simplification, direct impacts away from cities raise large amounts of fine dust high into the atmosphere; explosions over cities and forests may ignite gigantic plumes of fire that place clouds of coarser soot into lower atmospheric levels. Dust and soot block sunlight and engender nuclear winter. (I have not even mentioned scores of other profoundly negative effects, radiation and depletion of the ozone layer, for example.)

I cannot begin to handle the technical details in this short essay (the original TTAPS report and accompanying commentary by biologists, first published as two articles in
Science
, December 23, 1983, have been republished by W.W. Norton as
The Cold and the Dark
by Paul R. Ehrlich
et al.
—see bibliography. Carl Sagan also published a less technical, but still complete, account in the Winter 1983/84 issue of
Foreign Affairs
). I will, however, mention just two general conclusions. First, the threshold for nuclear winter can be reached by many plausible scenarios involving an appropriate percentage of the world’s megatonnage and a believable number of bombs exploded over cities and military targets. Second, and somewhat surprisingly, even a “small” nuclear war might, under plausible circumstances, trigger nuclear winter (for example, just 100 megatons, from our world supply of approximately 10,000, if exploded over cities with large subsequent fires and a maximal yield of soot, might suffice).

I am not an astute observer of world politics, and I was surprised (but quite pleased) that recognition of the possibility of nuclear winter has struck home with such force in so many quarters. I have always regarded our old scenario, restricted to the immediate consequences of blast and fallout, as so horrible that no increment of additional torment should be needed to galvanize public opinion. But I now realize, hopeful creatures that we are, how many people lived with the pipe dream view, now dispersed, that if they resided far enough from immediate blasts, and hunkered down long enough in their shelters, they could soon emerge into a shining world waiting to be rebuilt. I had also failed to recognize that people in other nations, particularly of the Southern Hemisphere, might have felt some personal safety, also now dispersed, in the face of northern madness. Nuclear winter also helps to clarify what seems to me the near certainty that any “conquest” in nuclear war could only become the ultimate Pyrrhic victory as an unforgiving climate propagates its chilling effects upon any aggressor.

In any case, the argument of nuclear winter has, like its dust cloud, spread throughout the world, bringing us all perhaps a bit closer and uniting us against a common peril—for the earth, like an organism, has its own continuity and can disperse evenly the insults that it suffers. The Pontifical Academy of Science, representing the world’s most ecumenical institution, brought twenty of us from eight nations and more religions (and nonreligions) to the Vatican to draft a statement about nuclear winter and to meet with Pope John Paul II in an effort to develop this new argument as an effective weapon against the threat of nuclear war. In a short statement to us, the pope argued that we must prevail by combining our scientific deterrent (our best estimate of the factual consequences) with the moral deterrent that he and others could supply. And I thought of the wedding of spiritual and temporal, contemplation and sensuality, physical power and moral persuasion, all pictured on the sixteenth-century ceilings of our meeting place. Continuity will require this flexibility, this joining of all our forces.