This video segment adapted from NOVA scienceNOW examines a developing theory that might explain a 250-million-year-old "murder mystery." While several possible causes have been considered for the mass extinction that occurred at the end of the Permian period, the scientists featured in the video think a chain of events, beginning with massive volcanic eruptions, might have made Earth uninhabitable for a significant number of terrestrial and marine organisms. According to their theory, these eruptions released gases that warmed both the atmosphere and the oceans. This warming in turn created ideal conditions for killer bacteria to poison the environment.

This video is available in both English and Spanish audio, along with corresponding closed captions.