Part biography and part scientific detective story, this debut by British science journalist Walker (a features editor for New Scientist) tells the story of Paul Hoffman, the brilliant, cantankerous Harvard geology professor most responsible for promoting the concept of "Snowball Earth." This controversial hypothesis asserts that about 600 million years ago, the entire planet was encased in ice that was thicker and lasted millennia longer than in any previously recognized ice age. Instantaneously in geologic time, the hypothesis continues, the planet moved from temperatures averaging minus 40 degrees centigrade to sweltering heat unlike anything seen since. These extreme climatic fluctuations may have been responsible for the origination of multicellular life at the beginning of the Cambrian Era and thus, ultimately, for most life on Earth today. Walker does a superb job of relating both the scientific and the human side of the controversy. Her prose, like her story, is likely to engage both scientists and general readers equally. All will be able to appreciate the importance of the issues while gaining greater insight into the process of scientific advances. Walker has written an important, provocative book that is a joy to read. Agent, Michael Carlisle.(Mar.)
