If you want some epic disaster tales this evening, you can watch this How Stuff Works podcastabout possible causes of the five mass extinctions that nearly extinguished all life on Earth. After that cheerful topic, I also talk about why scientists believe we're heading into a sixth mass extinction.
I've been obsessed with mass extinction for some time, and even wrote a book about it a couple years ago. What I'm discussing here are some of my favorite scientific hypotheses (sorry — I called them theories, but I meant hypotheses!) about what caused horrific mass extinctions in deep geological history. Understanding these previous events allows us to make judgements about whether we're in another mass extinction period right now. More importantly, it helps us figure out how we might stop the extinctions before they reach the epic levels required to qualify for a mass extinction.