The K-T event (Cretaceous-Tertiary event) refers to the mass extinction of the dinosaurs that took place approximately 65 million years ago (mya). In addition to the dinosaurs, most large land animals perished and an estimated 70% of all species on the planet became extinct.

In the early 1980s, a team of physicists and geologists documented a band of sedimentary rock in Italy that contained an unusually high level of the rare metal iridium (usually found on Earth's surface only as a result of meteor impacts). The scientists eventually argued that that the iridium layer was evidence of a large asteroid impact that spewed iridium contaminated dust into the atmosphere. Blown by global wind currents, the iridium eventually settled into the present thin sedimentary layer found at multiple sites around the world. Given the generalized dispersion of iridium the researchers argued that the impact was large and violent enough...