The Snowball Earth Hypothesis: Testing the Limits of Global Change

Some scientists believe that at one time in the past, Earth became so cold it completely froze over. This period of extreme cold was followed by a dramatic swing to warmth, which may have had a profound impact on the development of complex life on our planet. Other scientists disagree, questioning the Earth's ability to thaw and the survival of any life of its surface. Today on Focus, host David Inge talks to Paul Hoffman, professor of geology at Harvard University and one of the leaders of the "Snowball Earth" hypothesis.

Guest: Paul Hoffman (Sturgis Hooper Professor of Geology at Harvard University)