Snowball Earth: The Story of the Great Global Catastrophe that Spawned Life As We Know It. Gabrielle Walker. xviii + 269 pp. Crown Publishers, 2003. $24.95.
Imagine a world buried under more than a kilometer of ice—desolate and devoid of all but the simplest forms of life. Out of this frozen sea rise the peaks of volcanoes, which sporadically emit gases. Over millions of years these gases, some of which absorb radiant energy emitted from the icy surface, accumulate in the atmosphere. Temperatures gradually rise. The icy sheath catastrophically thaws, and eventually the world is steaming in a sauna—fresh, and ripe for an explosion of life. According to proponents of the Snowball Earth theory, which originated in the 1960s and was rejuvenated in the 1990s, this sequence of events unfolded repeatedly (perhaps as many as four times) on our planet roughly 600 to 700 million years ago.
This fantastic idea—"the most hotly contested theory in earth science today"—is described in dramatic fashion by Gabrielle Walker in Snowball Earth. Walker travels well beyond the confines of the academic debate and brings back gripping accounts of scientific adventures, tales of brawling geologists and wonderful descriptions of natural history. The book is a page-turner.
The story develops as Walker follows the life and career of the most outspoken advocate of the Snowball Earth theory, Harvard geologist Paul Hoffman. Surprisingly, the book provides more information about Hoffman's athletic prowess, personal relationships and lifetime ambitions than about swings in the Earth's climate in the distant past. He proves to be a delightful and worthwhile hero, though, exhibiting both an infuriating disregard for his colleagues and a passionate love of geology. Walker focuses on Hoffman and his personal crusade (often at the expense of junior scientists) to convince the world of the theory's validity; she observes that he seemed to be "trying to achieve the Snowball Revolution by the sheer force of his energy." This is a firsthand account of how a strong ego propels scientific discovery.
Although Walker notes Hoffman's fanatical obsession with his idea, she nonetheless idolizes him and champions his theory. She makes little attempt to provide alternative interpretations of the events preserved in the ancient rock record. In a few instances, opposing evidence is introduced, but only as a straw man to be neatly knocked down. Geologists who oppose the theory are derided as having been "taught from an early age that the Earth is a slow and steady place." This one-sided perspective makes for clean storytelling but ultimately sends a false message. Snowball Earth specialists will be disappointed in Walker's sterile account of a subject that has inspired many innovative ideas. Fortunately, Walker does richly portray the adventures and contributions of scientists who preceded Hoffman, including Louis Agassiz, Brian Harland and Joseph Kirschvink, showing clearly their crucial significance in the development of the theory.
In the course of narrating Hoffman's quest, Walker sneaks in a surprising amount of geological detail. A rudimentary understanding of the geology involved is fundamental to grasping the Snowball Earth concept, and Walker seamlessly introduces this information as a backdrop to, rather than an element of, the story line. The carbon cycle, global warming, paleomagnetism, ice ages, oolites, carbonates, fold tests, methane hydrates, beam depletion, the Cambrian explosion and plate tectonics are a few of the topics she covers, usually creatively. For example, she describes oolites as "a strange type of rock made up of tiny spheres that are squashed together like petrified caviar."
To see the evidence for climate swings, Walker trotted around the globe on field excursions to remote locations with expert geologists. The account of her encounter with an uneasy elephant is thoroughly entertaining, and her descriptions of natural history are marvelous, sometimes even lyrical. When she goes to Hamelin Pool in Australia in search of the microbial mats that are the modern, living equivalent of an ancient stromatolite (a fossil formed by layers of cyanobacteria), she notes that "shells of the beach crunch underfoot; they are tiny, bone-white, and perfectly formed, and the bivalves that grew them are eons of evolution ahead of the simple creatures that I'm seeking."
The book concludes with a doomsday warning that another Snowball Earth may lurk ahead, 350 million years in the future. Although intriguing, this idea is orders of magnitude more controversial than the Snowball Earth theory itself. Walker should have stopped there, but unfortunately she goes on to ask a rather contrived question: What will our descendants do? In light of current environmental concerns, the Chicken Little notion that an ice-covered Earth is coming seems irresponsible. Another problem, which is unavoidable, is that the book is already dated: Because of the considerable attention that the Snowball Earth controversy has provoked, in large part as a result of Hoffman's efforts, rapid scientific discoveries are being made. However, in light of the book's objectives—to inspire and entertain—this shortcoming is forgivable.
As an introduction for a general audience, Snowball Earth hits its mark; it is accessible and compelling. Even though she tells only half the story, Walker has crafted a book that is fascinating and enlightening.—Chris J. Poulsen, Earth Sciences, University of Southern California, Los Angeles