It's possible that within a decade, a space probe may swing into orbit around Europa and hurl a drill-tipped robot into its icy crust. If that turns out to be the case, no one will watch its performance more anxiously than Christopher Wills and Jeffrey Bada, the coauthors of The Spark of Life. As Europa orbits around Jupiter, the giant planet's gravity exerts enormous tidal forces on the moon with clock-like regularity-forces that Wills and Bada predict should create an environment favorable to the origin of life. If the probe does uncover some kind of indigenous life on Europa, it may bolster the central claim of this intriguing book: that similar processes made life possible on our own planet.