In the 1960s and 1970s, geology witnessed an intellectual revolution. Recognition that seafloors spread and continents drift led to plate tectonics. NNight Comes to the Cretaceous addresses a second, still developing revolution—the view that impact cratering and other catastrophes may be the dominant phenomena driving evolution of the biosphere. The specific case analyzed is the hypothesis of the late Nobel laureate physicist Luis Alvarez and his colleagues that the Cretaceous/Tertiary (K-T) mass extinctions resulted from the impact of a 10-km-wide asteroid or comet. Once Alan Hildebrand focused geologists' attentions on the immense Chicxulub crater in the Yucatan, K-T deposits bearing impact signatures were found to be arrayed radially to the crater, itself dated precisely at the K-T age of 65 million years. By the early 1990s, the Alvarez hypothesis was thereby proved, despite protests of a few holdouts, whose scientific sloppiness is repeatedly scorned by this book's author, James Powell, director of the Los Angeles County Museum of Natural History.