DinosaurAsteroidEvent-m-1124Five times in the history of Earth, life has been extinguished by cataclysmic events. In one of them, the K/T Extinction, a six-mile-wide asteroid wiped out the dinosaurs, and in the earlier Great Dying, fallout from massive volcanic eruptions annihilated 90 percent of the Earth’s species. Could it happen again? The Smithsonian Channel special “Mass Extinction: Life at the Brink” explains why and how these catastrophes occurred, and why humans now pose a greater threat to the planet than any geological disaster. The documentary, premiering Nov. 30, explains how human behavior and mistreatment of the planet mirrors the aftereffects of past mass extinctions. It notes that overpopulation leads to loss of plant and animal habitats and extinction of species, and global warming releases greenhouse gases, which acidify the ocean. Scientists estimate that most of the coral reefs will disappear by 2070, and many species of plants and animals, now heading toward extinction at 12 times the normal rate, will disappear. More