Celestial Sources of Terrestrial Mass Extinctions 1) National Geographic: What are mass extinctions and what causes them? 2) American Museum of Natural History: Episode Twelve: Six Extinctions in Six Minutes 3) BBC: Gamma-ray burst “hit Earth in 8th Century” 4) Nature: Gamma-ray burst linked to mass extinction 5) Phys.org: Researchers learn more about the possible […]