For almost 200 years, the idea of cosmic events affecting life on Earth was viewed as heretical by the church, which regarded catastrophe as proof of divine intervention, and as nonsense by the scientific establishment, which dismissed it as superstition. Yet in the end, the sheer weight of evidence has swept away all doubt about the reality of global catastrophes. Attempts to make scientific sense of the many legends of global catastrophes date back to the dawn of modern science itself, in the 17th century. Following the publication of Newton’s laws of motion and universal gravitation in 1687, Edmond Halley decided to apply them to the mystery of comets. By studying records of their appearance, Halley argued that the bright comets of 1456, 1531, 1607 and 1682 were in fact one comet, later known as the “Halley” comet, that followed a vast elliptical orbit around the Sun in agreement with Newton’s laws. But Halley noted something else as well: a comet crossing the orbit of the Earth might one day collide with us with devastating consequences.