Life After Ice
Thomas D. Cornell
E. C. Pielou. After the Ice Age: The Return of Life to Glaciated North America. 366 pp., illus., index. Chicago: University of Chicago Press, 1991.
Across the Finger Lakes region of New York State we have no trouble seeing signs of the Ice Age. To the south are the terminal moraines, vast piles of rubble that gave new definition to the divide between the Susquehanna and St. Lawrence Rivers. To the north are numerous drumlins, mounds whose alignments suggest the direction in which the ice moved. Then there are the lakes themselves, ancient valleys reshaped by the continental glaciers.
Of course, there is more to the region's landscape than just its geology. Also important is the richness of its plant and animal life. Yet how often have we asked ourselves: "If the entire region was once covered by several thousand feet of ice—ice powerful enough to have scoured out the Finger Lakes—then what happened to the region's wildlife, and where did the wildlife we see today come from?"
I confess that until recently such questions never occurred to me. To the extent that I gave the matter any thought at all, I adopted the general evolutionary point of view that different species had emerged at different times. Then I came across a book whose title alone was highly suggestive. Sure enough, as I began reading After the Ice Age: The Return of Life to Glaciated North America I found answers to those previously unasked questions.
But something else kept me going, page after page. From the dust jacket I learned that the author, Evelyn C. Peilou, was a scientist (a biologist, from Canada), and the way her book approached science reminded me that scientists should also be storytellers, that they should—from time to time—recast their specialized studies into narratives accessible to general audiences.
Americans have long tended to emphasize the practical applications of basic science—hence the emphasis today on new drugs, genetic engineering, solid-state electronics, computers, and so forth. Such applications have undeniable importance. But sometimes we forget that basic science has other "applications," as well. To a significant degree we rely upon basic science for a sense of who we are and why the world is the way it is. We have a need for scientific explanations, a need for "science stories."
In After the Ice Age, Pielou has deliberately sought to meet our need for "science stories." She has drawn upon a wide array of specialized studies to construct a general account of how plants and animals repopulated those regions purged of life by the ice.
The book opens with a brief overview of the Ice Age, describing the stages by which the ice drew back from its maximum extent some 18,000 years ago. Also in "Part One" (which is entitled "Preliminaries") Pielou discusses the kinds of evidence that scientists use when studying how the Ice Age affected life on the continent—evidence not only in the form of fossils but also in the form of the current geographical ranges of plant and animal species. In the process she explains the difficulties that scientists faced when proposing narratives about the past. "It is one thing," she points out (p. 61), "to collect and arrange a mass of raw material; it is quite another to interpret the mass and deduce from it a detailed, coherent, internally consistent, chronological 'story.'"
The chapters in "Part Two" survey what is known about living organisms at "The Time of Maximum Ice." One chapter examines what life might have been like to the south of the ice sheets. Another examines the coastal areas, where the ice coverage was probably not complete (leaving a handful of sites where plants and animals could survive). A third chapter examines the vast ice-free region that included portions of modern-day Alaska and Asia.
With the stage thus, set, the rest of the book ("Part Three: The Melting of the Ice," "Part Four: The Pleistocene/Holocene Transition," and "Part Five: Our Present Epoch, the Holocene") considers the possible sequence of events as the ice sheets shrank in size. The drama here is never lacking. Sometimes the tone is quiet—as in the case of tundra being replaced by open forests. At other times, the tone is intense—as in the rapid draining of vast glacial lakes after the collapse of ice barriers. There is even an occasional tone of mystery—notably in the discussion of a dramatic wave of extinctions that occurred toward the end of the Ice Age. Along with mastodons and saber-toothed tigers (to name two of the most familiar), the list of species that vanished included "the terrifyingly big, swift, agile, and ferocious short-faced bears" (p. 261):
In telling her story, the author has adopted a broad geographical scope. On the one hand, she makes reference to other parts of the world—noting, for example, in the book's "Prologue" that the change wrought by the Ice Age "has been greatest of all in northern North America, where the ice sheets of the last ice age were far larger (by fifty percent, at least) than those in Europe and Asia combined…"(p. 1). On the other hand, the book includes discussions of specific regions in North America—including the northeastern United States, as suggested by the following map (p. 93):
Another strength of the book is the breadth of its chronological scope. Not only does Pielou reach deeply into the geological past, but she also brings the story all the way to the present. "The most distinctive climatic interval of the recent past," she notes (p. 308) "is the Little Ice Age, which lasted from about 1350 to 1870 A. D.…" The period since then has been relatively warm. But what will the future bring? Has the next Ice Age already begun? Or will the Greenhouse Effect initiate a very different type of climatic change? These are questions that the author raises for our consideration in the book's "Epilogue."
The vast scope of the book—both geographical and chronological—is essential. Largely invisible in local areas and on a daily basis, the main outlines in Pielou's story come into clear focus only when distances can also be measured in hundreds (even thousands) of miles and when time can also be measured in centuries (and even millennia). In either case, the perspective is not one to which most of us are accustomed.
The illustrations included in this review suggest yet another strength of the book, namely, its use of visual material. At every step, the author has combined her written text with maps and line drawings to help the reader form an imaginative picture of the developments and situations she describes.
In writing After the Ice Age: The Return of Life to Glaciated North America, Pielou has chosen a difficult task for herself. That she succeeds so well testifies both to her skill as a scientist and to her skill as a storyteller. — Thomas D. Cornell
The different refugia, and different migration speeds, of four species of tree. Maple and chestnut spread north from an area around the mouth of the Mississippi; eastern white pine and eastern hemlock, from the east coast. The lengths of the arrows are proportional to their speeds of advance. The shading shows the area in which the ranges of all four species overlap at the present day. Reprinted by permission from the University of Chicago Press.