View full lesson: http://ed.ted.com/lessons/earth-s-mass-extinction-peter-ward

Asteroid strikes get all the coverage, but "Medea Hypothesis" author Peter Ward argues that most of Earth's mass extinctions were caused by lowly bacteria. The culprit, a poison called hydrogen sulfide, may have an interesting application in medicine.

Talk by Peter Ward.

Learn more about your ad choices. Visit megaphone.fm/adchoices