About 65 million years ago, three-quarters of all species alive on earth at the time died out within the space of a few hundred thousand years. The dead included every one of the mighty dinosaurs, which had dominated for some 60 million years. Their passing paved the way for the rise of the birds, mammals, and, ultimately, the emergence of humankind.

Intriguingly, a similar mass extinction has ushered in the reign of the dinosaurs. Indeed, over the last 600 million years of life on earth, there seems to have been a cataclysmic change roughly every 60 to 70 million years, and smaller changes roughly every 30 million.

As soon as scientists who study the early history of life – paleontologists – identified this pattern, they began to search for a cause. Many theories have been put forward, but in 1980 the geologist Walter Alvarez and his Nobel Prize-winning father, Luis, startled the scientific world with a new theory that, for a time, swept all others aside.