Gabrielle Walker’s Snowball Earth: The Story of the Great Global Catastrophe That Spawned Life As We Know It focuses on the steps taken by Harvard University geoscientist Paul Hoffman to prove a theory that multicellular life evolved from a climatic catastrophe that began over 700 million years ago. The “snowball Earth theory,” originally proposed by geologist Joe Kirschvink at the California Institute of Technology, is based on the premise that the Earth was encased in ice between 750 and 590 million years ago. Eventually, volcanoes vented sufficient amounts of carbon dioxide into the atmosphere to produce a global greenhouse effect, melting the ice and causing the Earth to heat up dramatically. Now exposed to sunlight, the primitive organisms in the seas began to evolve into complex life forms, a time known as the Cambrian explosion.
Walker vividly describes field sites around the world where geological evidence has been gathered by Hoffman and others to collaborate their snowball theory of the Earth. She herself has visited many of the sites, making her dialogue more real and interesting. Written in novel form, the book provides both a biography of Hoffman, as well as some exposure to scientific research, exploration, discovery, and debate.
Although the book brings a better understanding of modern scientific developments to the lay reader, it is rather shallow in scientific content. The scientific evidence for the radical “snowball Earth theory” is very incomplete. No accepted explanation exists for how the Earth could have frozen in the first place. Unfortunately, Walker promotes the snowball theory and leaves the reader with the impression that it is the only plausible theory leading to the evolution of complex life forms on the Earth.