A persistent cultural stereotype of scientists is that we are out to dominate and exploit the natural world that we study. In Life on a Young Planet, distinguished paleontologist Andrew Knoll wants to turn this stereotype on its head, replacing scientist-as-conquistador with scientist-as-steward. In the opening pages, he writes, "by coming to grips with life's long evolutionary history, we begin to understand something of our own place in the world, including our responsibility as planetary stewards." Knoll has set out to write nothing less than a narrative history of how life arose on Earth—"science's creation story," he calls it—assuming, or at least hoping, that if we know the story, we will see that it is humanity's job to preserve the rich diversity of life on Earth which is presently our inheritance.

Knoll begins his book by challenging another cultural stereotype: the pedantic scientist who reduces marvelous phenomena to sterile terms. To Knoll, the findings of his field are exciting and wonderful, and he hopes to share that wonder with his readers. Of course, this is to exchange one stereotype for another—the scientist as Impresario of Wonder—but Knoll's writing is eloquent and engaging, and the story is a fascinating one. How did the Earth's atmosphere go from being rich in sulfur to being rich in oxygen, without which life as we know it today could not survive? How did life arise from nonliving chemicals? What was the nature of those first life forms? How did those first life forms develop into the amazing variety of complex creatures we see today that inhabit nearly every imaginable niche of our planet—even hot springs and chasms deep in the sea floor? While much remains to be understood about each of these questions, what is known is amazing.

The ingenuity of paleontologists is also impressive. Knoll describes the methods as well as the findings of his field, showing us how he and his colleagues deduce the story from the many kinds of records that early life has left us, from fossils to the DNA of today's creatures. The story of the rise of early life is interspersed with descriptions of the research process that both illustrate the vast range of methods employed and lend a human concreteness to the discoveries. For example, Chapter 6 opens with an anecdote from Knoll's graduate studies with groundbreaking paleontologist Elso Barghoorn:

"Take a good chunk. You never know when you'll be back." With that admonition, Elso Barghoorn heaved a fifty-pound block of chert into our aluminum dinghy, beached on a rocky promontory along the north shore of Lake Superior.

Seeking to pump up "human interest," many books for the non-expert reveal and at times exaggerate the competition and egotism that are unfortunately far too common in science. Life on a Young Planet is refreshingly, even remarkably, free of any sense of jostling for position. Knoll describes his own contributions with humility, praises the insightfulness and hard work of his mentors and colleagues, and portrays the community of paleontologists in warm and affectionate terms. (As a scientist myself, though in a very different field, I find myself wondering if it can really be as good as Knoll makes it sound!)

Life on a Young Planet is not entirely successful as a primer in paleontology for the average reader. To trace the development of life on Earth, Knoll must cover an enormous range of scientific terrain, including the geology, atmospheric chemistry, and oceanography of the early Earth as well as the biology of the organisms that inhabited it. Before the story can really take off, a great deal of background must be established. Consequently, the early chapters are dense and lack a clear narrative shape. Each chapter begins with a paragraph-long summary; I often found I needed to return to the summary a few times in the course of reading the chapter to understand where the chapter was going. Vocabulary is also a problem. This history of early life overflows with creatures, phenomena, and ideas, and Knoll assumes a familiarity with both concepts and vocabulary that I doubt most readers have, using technical terms interchangeably with more common synonyms without making the correspondence clear.

At about chapter 8, however, "The Origins of Eucaryotic Cells," the book finds its narrative stride, and from there on, the story line is clearer and more compelling. Chapter 8 itself is particularly strong. It begins with the story of the discovery of how eucaryotic cells (cells with nuclei) came to have metabolic organelles inside them. (In plant cells, the conversion of sunlight and carbon dioxide to oxygen and sugars, photosynthesis, takes place in chloroplasts; in animal cells, the conversion of oxygen and sugars to carbon dioxide and energy-storing molecules, respiration, takes place in mitochondria.) It is now accepted that the organelles were originally independent bacteria, engulfed by another cell. But Knoll does more than just give this explanation; he tells us how this idea was first proposed by Konstantin Merezhkovsky in 1905, but dismissed because the experimental evidence did not seem consistent. More than 60 years later, Lynn Margulis proposed the same idea independently for a different type of cells, and the new techniques of molecular biology were able to verify it. This chapter is filled with the excitement of a revolutionary change in thinking.

The bulk of Knoll's narrative ends with describing the conditions that gave rise to the sudden rapid development of many types of multicellular animals. Chapter 12, "Dynamic Earth, Permissive Ecology," lays out the thesis that this remarkable diversification—known to geologists as the Cambrian Explosion because of the dramatic increase in the number of observed fossil species in the Cambrian period—took place when the ecology of the Earth was undergoing equally dramatic changes: "extreme environmental stress can induce mutations that fuel biological innovation." Changes in the amount of oxygen in the atmosphere and oceans may have been particularly crucial in allowing larger, more differentiated animals to arise. At the same time, the presence of animals had a reciprocal impact on the surrounding environment. "Life and environment evolved together," Knoll concludes, "each influencing the other in building the biosphere we inhabit today."

Throughout Life on a Young Planet, Knoll connects his writing repeatedly to creation stories, using biblically allusive language, but he generally avoids giving metaphysical interpretations of the scientific findings he describes. Not until the epilogue does he directly tackle the relationship between science and religion. Here, Knoll takes a generally friendly stance toward religion; while he strongly rejects a literal reading of Genesis on the grounds that it is contradicted not only by his own field but also by central findings of astronomy, physics, and geology, he advocates a complementary approach to religious and scientific understanding of the universe, with science revealing what took place and religion why it took place:

The great creation stories of the Bible, or the Upanishads, or the Aboriginal Dreamtime, provided ways of comprehending the universe thousands of years before Copernicus, Newton, Darwin, or Einstein provided new explanatory language. As eloquent guides to a moral universe, they continue to speak across the generations.

"Science's creation story," he adds, "accounts for process and history, not intent," and he rightly points out that while science places some limits on what religious accounts can be believed, the daily tragedies of human existence issue far greater challenges to our understanding of how a loving God can be sovereign over our planet.

But in declaring that questions of morality and purpose are the terrain of religion rather than science, Knoll exposes, perhaps unwittingly, why this book does not achieve its first stated goal: to persuade the reader that it is our job as humans to steward the earth. Earlier in the epilogue, he argues that human beings occupy a unique position in life's history, not because humanity is in some way the culmination of evolution, but rather because we possess the power, through technology, to profoundly shape the future of life on our planet in a way no other species can.

At this point, Knoll needs to show us that the history of life itself persuades us to use our formidable power in a particular way—to preserve the diversity that presently exists. But such persuasion is notably absent. The most he can say is, "I don't know whether God decreed the passenger pigeon, but if he did, it was not for us to exterminate." I agree with Knoll that science's story on its own is devoid of intent. Consequently, contrary to what Knoll seems to think, it offers no moral guidance. Science's story, however awe-inspiring, does not point to any particular way—much less the best way—to use our power.

In Knoll's picture, we have complete responsibility for the future of the planet. This inspires the final plea that closes the book:

On this planet, at this moment in time, human beings reign. Regardless of who or what penned earlier chapters in the history of life, we will write the next one. Through our actions or inaction, we decide the world that our grandchildren and great-grandchildren will know. Let us have the grace and humility to choose well.

Fortunately, the biblical narrative tells us that we do not have to make our choices alone. If human beings really did write the next chapter of our planet's history unaided, it would be bleak indeed. But if the universe is actually sustained and directed by its Creator, there is reason to believe our planet can recover from some of our mistakes. And worship of that Creator, not just wonder at the creation, can generate the grace and humility that Knoll invokes. There is still hope that we will not completely remake our planet in our own image, with the lifelessness that would surely come if the last word were ours.

Catherine H. Crouch is an assistant professor of physics at Swarthmore College.

Copyright © 2003 by the author or Christianity Today/Books & Culture magazine.
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