Science

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Christine Todd Whitman, head of the Environmental Protection Agency, is leaving her post after more than two years of highly charged debates that often put her at odds with others in the Bush administration. Experts examine President Bush's environmental record…

Ray Suarez reports on the findings and remaining questions in the space shuttle Columbia disaster investigation and then follows up in a discussion with Jerry Grey of the American Institute of Astronautics and Donna Shirley of the University of Oklahoma.

Margaret Warner discusses DNA with Eric Lander, director of the Whitehead Institute's Center for Genome Research in Cambridge, Massachusetts, and a representative of the Human Genome Project.