Walter Alvarez and his dad came up with the theory and then worked to find the evidence of the impact theory for the K-T mass exinction This book provides a step-by-step through that mystery - from dating fossils and layers, to the excess of iridium, to the discovery and confirmation of the Chicxulub impact site. In case you want to know what it was like for T. Rex, the first chapter provides a blow-by-blow of the object slamming into the earth, melting bedrock and changing the climate in one punch. Accessible to non-scientists, this history is a tad dry, but definitely recommended.