In 1980, Walter Alvarez, a geologist at the University of California, Berkeley, and his colleagues proposed that the dinosaurs had been exterminated by an asteroid that smashed into the Earth. I was fourteen at the time, and that mix of dinosaurs, asteroids, and apocalyptic explosions was impossible to resist. I can still see the pictures that appeared in magazines and books–paintings of crooked rocks crashing into Earth, sometimes seen from the heavens, sometimes from the point of view of an about-to-become-extinct dinosaur. Suddenly the history of life was more cinematic than any science fiction movie.By luck rather than foresight, I eventually became a science writer. I had the good fortune to start the job in the early 1990s, as the