A whiteboard video on the U.S. Constitution and Bill of Rights.

The United Nations believes that there are at least three million shipwrecks on the ocean floors, sparking a centuries-long obsession with these sunken vessels and the wealth they might carry.

Sam dives deep to discover Shipwreck Reef, where shipwrecks have transformed into an artificial reef system that helps the habitat. Find out why the reef exists in this episode of "What Sam Sees."

While serving in the military, Jackie Robinson was arrested for refusing to move to the back of a segregated bus. In 1947, he made history when his debut with the Brooklyn Dodgers ended racial segregation in Major League Baseball.