Fire on Earth: Doomsday, Dinosaurs, and Humankind

A crater discovered in Mexico's Yucatan Peninsula in 1978, and intensively investigated in 1990, may provide the ""smoking gun"" confirming that the extinction of the dinosaurs was caused by a meteorite that smashed into Earth 65 million years ago, wiping out 70% of all plant and animal species. The Gribbins, popular science writers, consider the evidence for this theory overwhelming. Collisions with comets, scientists now believe, have resulted in mass extinctions on Earth every 26 to 30 million years. Lesser cosmic impacts, the Gribbins hypothesize, shaped the evolution of human civilization by triggering ice ages. The Tunguska explosion of 1908, which produced a devastating fireball in Siberia that destroyed forests and caused worldwide tremors, was the result of an asteroid or meteor, they believe. More speculative is their proposal that a cataclysmic collision triggered the collapse of Roman Britain around A.D 500. Fragments of the Shoemaker-Levy comet rammed into Jupiter in 1994. To monitor the possibility of similar catastrophes on our planet, the Gribbins strongly endorse NASA's proposed Spaceguard Survey, a scheme to identify threatening asteroids and comets using a network of as-yet-unbuilt telescopes. Free of sensationalism, this is popular science writing at its most lucid and entertaining. (July)