Mercury is a planetary ""baked Alaska"" . . . Velikovsky is undoubtedly wrong, but we are probably moving toward a synthesis of catastrophism and uniformitarianism. . . ten or fifteen years ago global plate tectonics was heresy, today it is The Paradigm. . . these are some of the observations and musings of Clark Chapman, a planetologist (specialist in Mercury) at the Planetary Science Institute in Tucson, Arizona. In this short book he reviews present knowledge of the inner ""terrestrial"" planets (Mercury, Venus, Mars, and Earth), adds a summary of what the Apollo program contributed to our knowledge of the moon, and speculates on the history of the asteroids, which, because of their age, may provide essential clues to the origin of the solar system itself. Chapman's treatment of the facts differs from most popular summaries in its comparative approach. He groups Earth, Mars, and Venus together, remarking on their similarities in size and absorption of solar energy, and points out how subtle differences in temperature and chemical interactions have led to their present widely divergent surface conditions: the Earth compatible with life; Venus with its intense heat and blanket of sulfuric acid clouds and carbon dioxide; Mars with its thin atmosphere and chilly, moon-dead topography. And the glance back at what past geologists or astronomers have thought and how rapidly ideas have changed (not only because of the space program but also because of radar astronomy or spectrophotometry) is an intriguing lesson in the history of science. Notwithstanding its brevity, this book packs in an enormous amount of information, and one can only admire the style and sophistication with which Chapman manages it all.