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Introduction: The What, When, and How of Life’s Beginnings
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introduction The What, When, and How of Life’s Beginnings j. william schopf In this news-conscious age, everyone knows the journalist’s litany of prime questions: who, what, when, where, why, how. About the origin of life, scientists’ questions are similar, but more restricted. Setting aside the who (no humans were on hand to observe the event), the where (unanswerable except in the broadest terms—on Earth, in water, probably in oceans), and the why (a question posed by philosophers and theologians , not scientists), we are left with the three great puzzles this volume addresses: What is the origin of life, when did it begin, and how? At first blush, the what seems easy to answer: Surely, we can posit a primal protoplasmic globule, a first speck of living matter. But the answer is not so simple. Just as the colors of a rainbow merge imperceptibly one into another, the transition to life from nonlife is a seamless continuum . Some researchers define life as an interacting combination of a particular set of chemicals. Others consider it a highly ordered, intricately complex information-processing system. Still others insist upon a full-blown living cell. Consensus is elusive. Although the extremes of the continuum are sharp and clear, the dividing line between nonlife and life is blurred. Surprisingly, deciphering the when of life’s beginnings is even more vexing. Life’s origin ought to be easy to date—trace the fossil record back to a time when the record peters out, and, voilà, that’s when life began. But Nature has proven uncooperative, for it is the rock record that peters out, not the evidence of life. Over time, Earth’s rock record 1 2 Introduction has been weathered away and lost by the geologic cycle of uplift, erosion , burial, and pressure-cooking (followed by more uplift, erosion, burial, and cooking); thus, few traces of the planet’s early history are left today. However, of the slivers of ancient terrains that do remain, most contain traces of life. This is important knowledge. By telling us that life started remarkably early in the history of the planet, it suggests that life’s origin happened more quickly—and much more easily—than we otherwise might have imagined. But it has a downside. Hidden deep in the recesses of Earth’s past, dating from a time for which no surviving rocks can tell the story, hard evidence not only of life’s beginning but the life-generating event itself seems lost forever. Of the three great puzzles, the how of life’s beginnings has been plumbed most deeply. But here, too, the answer is hazy. (Were it not, the names of the Nobel Prize–winning researchers would be familiar to us all and this book would be quaintly dated.) But given the depth of this problem and the role it plays in understanding where living systems (humans included) fit in the natural order, it is not surprising that this great mystery is as yet unsolved. Until fairly recently, the origin of life was sacrosanct territory, the exclusive province of theologians. These limits were breached in 1953 when Stanley Miller announced a breakthrough discovery. He showed that amino acids like those present in living systems can be made easily , in a matter of days, from very simple ingredients, in the total absence of life. Carried out under conditions designed to mimic those of the primitive Earth, his experiments were the first to show a plausible way that potentially life-generating organic molecules could have formed before life got started. Yet even with this impetus, the subject remained taboo in some quarters. For example, the late Sidney Fox, a pioneer in origin-of-life studies, liked to remind his colleagues that in the mid1950s , the fledgling National Science Foundation refused his request for funding—not on scientific grounds, but to avoid being torn asunder by fundamentalists in Congress. Since that time, the origin of life has gained its rightful place among the great unsolved questions of science. Ironically, however, the flood of new research has pointed up just how complicated the problem is. This, too, is unsurprising. In science, the devil is often in the details: Time and again, simple, first-found solutions turn to dust as further work uncovers new layers of unexpected complexity. Savants have long pondered what life is and how it differs from inanimate matter. How did the ancients explain its origin? How and by [52.91.255.225] Project...