Summary

Extinction of the dinosaurs ("those magnificent animals") was caused by a meteoroid impact 66 million years ago "through no fault of their own," which makes clear the connection between terrestrial and extraterrestrial occurrences, according to Randall. "A disk of dark matter in the plane of the Milky Way was theoretically responsible for triggering the meteoroid's fatal trajectory." Randall traces the gradual human understanding of how the collision of off-earth objects affected evolution of species as well as the geologic composition of limestone layers that mark different epochs in earth's history.

In 1980, father-son scientists Luis and Walter Alvarez led a team from the University of California, Berkeley who determined that dramatic variations in limestone layers included high levels of iridium—an element relatively rare on earth but scattered throughout the solar system. In various locations around the earth, the scientists...