It's death on an unimaginable scale, when a majority of Earth's species quickly die out. It's called "mass extinction," and it's happened at least five times before. Cataclysms, such as supervolcanoes or asteroids, are thought to cause these events, but some experts believe a manmade mass extinction could be next. Is our planet in trouble? And if so, is there anything we can do to stop the next catastrophic annihilation?... see more