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Among the growing collection of thoughtful and thought-provoking books on extraterrestrial life, University of Colorado geology professor Jakosky's targets the most academic readers. This scholarly but readable presentation enables readers to pursue their questions in depth. The book's organization reflects its origin as an undergraduate course called "Extraterrestrial Life." Each chapter reads like a self-contained lecture that builds carefully on the preceding ones. Most end with a section called "Concluding comments" that reminds the reader of a skilled instructor's lecture summary, tying threads of evidence together yet leaving open questions for the next class period.
After opening with a discussion of the development of and requirements for terrestrial life, Jakosky takes his readers on a tour of the universe, steadily progressing toward more speculative venues. The first stop is Mars and the controversial evidence of bacterial life there in ancient epochs. From there, it is onward to Venus, the satellites of Jupiter and Saturn, and then to possible terrestrial planets in orbit around other stars. We now know that such planets are likely to exist, but are habitable environments common? Is biology rare, or is life an opportunistic and tenacious phenomenon, almost certain to spring up where conditions are right? If life forms, is intelligence a natural consequence?
The excitement of those questions, says Jakosky, is not that the answers are at hand, but rather that the quest has moved from theory to observation and experiment. He leaves his readers eagerly awaiting the next discoveries.