About 65 million years ago, the catastrophic impact of a comet on the coast of Yucatan in Mexico resulted in the extinction of almost all vertebrates on Earth, including all dinosaurs. Could it  be that such an event was triggered by the existence of a dark matter disk in our galaxy? A disk made of particles completely different from the ones that form our own bodies or anything else we have ever directly observed? This is the speculative proposal made by the Harvard theoretical physicist Lisa Randall in Dark Matter and the Dinosaurs.

Her book is divided into three parts. The first is an introduction to cosmology, the history of the universe, and how astronomers have come to work out that dark matter exists and its importance in the formation of galaxies. The second covers the solar system, how it was formed, and the orbits and composition of asteroids and comets, as well as providing detailed evidence from geology of fossils, extinctions and meteorite impacts. In the third, Randall presents possible candidates for dark matter, and how her particular model, fitting all the current data, could explain a thin dark matter disk in the plane of the galaxy. This disk, she argues, could periodically distort the path of icy objects orbiting the Sun very far away, in the Oort cloud, sending some of them into the solar system as comets.

Dark Matter and the Dinosaurs is a book for people who would like to meet a university professor for hours in a quiet corner cafe. Randall explains all the details to you, punctuating the conversation with anecdotes about her trips and encounters with her fellow scientists. The text is engaging, if a bit repetitive. It will be fascinating to see whether her thesis is supported by data currently being collected by the Gaia space observatory.