Earth's mass extinction - Peter Ward

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