Sixty-five million years ago, about 70 percent of all species then living on Earth disappeared within a very short period. ... Paleontologists speculated and theorized for many years about what could have caused this mass extinction, known as the K-T event (Cretaceous-Tertiary Mass Extinction event). ... The Alvarez team suggested that the enhancement was the product of a huge asteroid impact. ... Sulfuric acid aerosols may have cooled Earth for years. ... Appendix C ...