Epilogue

Whispers from the Grave

By now, it should be evident that these fascinating creatures called dinosaurs played a pivotal role in Earth's history. Perhaps your newfound knowledge of dinosaurs will enter conversation at parties or serve you in trivia contests with the youngsters in your life. Yet you might reasonably ask (as many have asked me), "What relevance do dinosaurs have today?" Do they serve any utility beyond their entertainment value? Let me try to persuade you that dinosaurs still have much to teach us, if we care to listen.

I'll begin my case with what may seem an outlandish claim:

Dinosaurs may well be crucial to the continued existence of humanity and much of the planet's biodiversity.

"Sure," I can hear you saying, "spoken like a true paleontologist." But consider this. The asteroid impact (Silver Bullet) hypothesis was put forth to account for the end-Cretaceous extinction of dinosaurs. Scientific study of this impact scenario led to a frightening realization: a future comet or asteroid strike could decimate human civilization and result in the extinction of millions of species, possibly even our own. Research has shown that such near-Earth objects (NEOs) pose a remote but very real threat; collisions with an asteroid greater than 1 kilometer (0.6 mile) in diameter (large enough to generate global havoc) occur every few hundred thousand years or so. In the wake of this insight, research programs led by NASA and other space agencies investigate technological avenues both for the detection and deflection of NEOs. In a related vein, study of the K-T "impact winter" scenario—that is, the global fallout resulting from a major asteroid strike—helped define the "nuclear winter" scenario— the global catastrophe that could follow an all-out exchange of thermonuclear weapons. The latter idea, presented to the U.S. Congress by such well-known scientists as Carl Sagan, has been a profound deterrent for those who might contemplate such military madness. Therefore, it's entirely feasible that dinosaurs, or at least their modern-day study by geologists and paleontologists, might one day be regarded as an important element in the persistence of humanity. This conclusion underscores the diverse interconnections binding the physical and biological realms, as well as the importance of pure research, which often yields unexpected outcomes.

There's another way in which dinosaurs just might help "save" our world. We live at arguably the most pivotal moment in human history. Overwhelming scientific consensus confirms that we've reached a tipping point in our relationship with the natural world, approaching (and, in some cases, exceeding) the limits of the biosphere to absorb the excesses of human existence.

To focus on a single aspect of this crisis—loss of biodiversity—Earth's biosphere is currently home to an estimated 13 million species. Biologists have formally named and described fewer than 2 million of these, with an overwhelming emphasis on larger, conspicuous critters. Between 10 and 40 percent of all species (including one in four varieties of mammals) are now threatened, with the numbers of imperiled life-forms rising rapidly. Over the past century, the pace of species extinction has skyrocketed, with recent estimates indicating a rate approaching a thousand times greater than prehuman levels! Paleontologists see evidence in the fossil record of five previous mass extinctions, and we are now on the brink of the sixth such cataclysm—the largest extinction event since the one that killed off the dinosaurs over 65 million years ago. The present panoply of biodiversity, the product of millions of years of evolution, is being wiped out in mere decades, an undetectable blip on the radar screen of deep time. If the current extinction trend continues, about half of all species alive today may be extinguished by the close of this century, with uncertain consequences for the survivors.

A unique aspect of this particular mass extinction is its precipitation by a single species— us. This time around, humans are the asteroid on a collision course with Earth. A recent assessment of global ecosystems—sponsored by the United Nations and carried out by 170 scientists from an array of disciplines—concluded overwhelmingly that this ecological crisis is being driven by human activities. The report's statistics are staggering: almost 60 percent of coral reefs threatened, more than half of the world's wetlands destroyed, 80 percent of grasslands imperiled, and 20 percent of drylands in danger of becoming desert. Causes of this dramatic, widespread environmental degradation are all too familiar to most readers: deforestation, human overpopulation, spread of toxic pollutants, overexploitation of animal species, and emission of greenhouse gases leading to global warming. Nature has simply been unable to absorb the punishment delivered by ballooning human populations and increasing consumption linked to industrialization.

Yet, despite the severity of this ecocrisis, we continue to spend our environmental "capital" like some crazed gambler unable to see beyond the next hand of Texas Hold'em. Without a rapid and radical shift in global priorities, we're headed for ecological bankruptcy, and the effects of this stunning environmental "downturn" will be felt much longer than any

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